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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MMUSIC Working Group C. Holmberg 3 Internet-Draft Ericsson 4 Updates: 3264 (if approved) H. Alvestrand 5 Intended status: Standards Track Google 6 Expires: March 4, 2018 C. Jennings 7 Cisco 8 August 31, 2017 10 Negotiating Media Multiplexing Using the Session Description Protocol 11 (SDP) 12 draft-ietf-mmusic-sdp-bundle-negotiation-39.txt 14 Abstract 16 This specification defines a new Session Description Protocol (SDP) 17 Grouping Framework extension, 'BUNDLE'. The extension can be used 18 with the SDP Offer/Answer mechanism to negotiate the usage of a 19 single address:port combination (BUNDLE address) for receiving media, 20 referred to as bundled media, specified by multiple SDP media 21 descriptions ("m=" lines). 23 To assist endpoints in negotiating the use of bundle this 24 specification defines a new SDP attribute, 'bundle-only', which can 25 be used to request that specific media is only used if bundled. The 26 specification also updates RFC 3264, to allow usage of zero port 27 values without meaning that media is rejected. 29 There are multiple ways to correlate the bundled RTP packets with the 30 appropriate media descriptions. This specification defines a new 31 Real-time Transport Protocol (RTP) source description (SDES) item and 32 a new RTP header extension that provides an additional way to do this 33 correlation by using them to carry a value that associates the RTP/ 34 RTCP packets with a specific media description. 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at http://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on March 4, 2018. 53 Copyright Notice 55 Copyright (c) 2017 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 This document may contain material from IETF Documents or IETF 69 Contributions published or made publicly available before November 70 10, 2008. The person(s) controlling the copyright in some of this 71 material may not have granted the IETF Trust the right to allow 72 modifications of such material outside the IETF Standards Process. 73 Without obtaining an adequate license from the person(s) controlling 74 the copyright in such materials, this document may not be modified 75 outside the IETF Standards Process, and derivative works of it may 76 not be created outside the IETF Standards Process, except to format 77 it for publication as an RFC or to translate it into languages other 78 than English. 80 Table of Contents 82 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 83 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 84 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7 85 4. Applicability Statement . . . . . . . . . . . . . . . . . . . 7 86 5. SDP Grouping Framework BUNDLE Extension . . . . . . . . . . . 7 87 6. SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . . 8 88 7. SDP Information Considerations . . . . . . . . . . . . . . . 9 89 7.1. Connection Data (c=) . . . . . . . . . . . . . . . . . . 9 90 7.2. Bandwidth (b=) . . . . . . . . . . . . . . . . . . . . . 9 91 8. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 9 92 8.1. Mux Category Considerations . . . . . . . . . . . . . . . 10 93 8.2. Generating the Initial SDP Offer . . . . . . . . . . . . 10 94 8.2.1. Suggesting the offerer BUNDLE address . . . . . . . . 11 95 8.2.2. Example: Initial SDP Offer . . . . . . . . . . . . . 11 97 8.3. Generating the SDP Answer . . . . . . . . . . . . . . . . 12 98 8.3.1. Answerer Selection of Offerer Bundle Address . . . . 13 99 8.3.2. Answerer Selection of Answerer BUNDLE Address . . . . 14 100 8.3.3. Moving A Media Description Out Of A BUNDLE Group . . 14 101 8.3.4. Rejecting A Media Description In A BUNDLE Group . . . 15 102 8.3.5. Example: SDP Answer . . . . . . . . . . . . . . . . . 15 103 8.4. Offerer Processing of the SDP Answer . . . . . . . . . . 15 104 8.5. Modifying the Session . . . . . . . . . . . . . . . . . . 16 105 8.5.1. Suggesting a new offerer BUNDLE address . . . . . . . 16 106 8.5.2. Adding a media description to a BUNDLE group . . . . 17 107 8.5.3. Moving A Media Description Out Of A BUNDLE Group . . 17 108 8.5.4. Disabling A Media Description In A BUNDLE Group . . . 18 109 9. Protocol Identification . . . . . . . . . . . . . . . . . . . 18 110 9.1. STUN, DTLS, SRTP . . . . . . . . . . . . . . . . . . . . 19 111 10. RTP Considerations . . . . . . . . . . . . . . . . . . . . . 19 112 10.1. Single RTP Session . . . . . . . . . . . . . . . . . . . 19 113 10.1.1. Payload Type (PT) Value Reuse . . . . . . . . . . . 20 114 10.2. Associating RTP/RTCP Streams With Correct SDP Media 115 Description . . . . . . . . . . . . . . . . . . . . . . 20 116 10.3. RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . 26 117 10.3.1. SDP Offer/Answer Procedures . . . . . . . . . . . . 26 118 11. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 28 119 11.1. SDP Offer/Answer Procedures . . . . . . . . . . . . . . 29 120 11.1.1. Generating the Initial SDP Offer . . . . . . . . . . 30 121 11.1.2. Generating the SDP Answer . . . . . . . . . . . . . 30 122 11.1.3. Offerer Processing of the SDP Answer . . . . . . . . 30 123 11.1.4. Modifying the Session . . . . . . . . . . . . . . . 30 124 12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 30 125 13. RTP Header Extensions Consideration . . . . . . . . . . . . . 31 126 14. Update to RFC 3264 . . . . . . . . . . . . . . . . . . . . . 31 127 14.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 31 128 14.2. New text replacing section 5.1 (2nd paragraph) of RFC 129 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 130 14.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 32 131 14.4. New text replacing section 8.2 (2nd paragraph) of RFC 132 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 133 14.5. Original text of section 8.4 (6th paragraph) of RFC 3264 32 134 14.6. New text replacing section 8.4 (6th paragraph) of RFC 135 3264 . . . . . . . . . . . . . . . . . . . . . . . . . . 33 136 15. RTP/RTCP extensions for identification-tag transport . . . . 33 137 15.1. RTCP MID SDES Item . . . . . . . . . . . . . . . . . . . 34 138 15.2. RTP SDES Header Extension For MID . . . . . . . . . . . 34 139 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 140 16.1. New SDES item . . . . . . . . . . . . . . . . . . . . . 35 141 16.2. New RTP SDES Header Extension URI . . . . . . . . . . . 35 142 16.3. New SDP Attribute . . . . . . . . . . . . . . . . . . . 36 143 16.4. New SDP Group Semantics . . . . . . . . . . . . . . . . 36 144 17. Security Considerations . . . . . . . . . . . . . . . . . . . 37 145 18. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 38 146 18.1. Example: Bundle Address Selection . . . . . . . . . . . 38 147 18.2. Example: BUNDLE Extension Rejected . . . . . . . . . . . 40 148 18.3. Example: Offerer Adds A Media Description To A BUNDLE 149 Group . . . . . . . . . . . . . . . . . . . . . . . . . 41 150 18.4. Example: Offerer Moves A Media Description Out Of A 151 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 43 152 18.5. Example: Offerer Disables A Media Description Within A 153 BUNDLE Group . . . . . . . . . . . . . . . . . . . . . . 45 154 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 46 155 20. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 47 156 21. References . . . . . . . . . . . . . . . . . . . . . . . . . 56 157 21.1. Normative References . . . . . . . . . . . . . . . . . . 56 158 21.2. Informative References . . . . . . . . . . . . . . . . . 58 159 Appendix A. Design Considerations . . . . . . . . . . . . . . . 59 160 A.1. UA Interoperability . . . . . . . . . . . . . . . . . . . 59 161 A.2. Usage of port number value zero . . . . . . . . . . . . . 61 162 A.3. B2BUA And Proxy Interoperability . . . . . . . . . . . . 61 163 A.3.1. Traffic Policing . . . . . . . . . . . . . . . . . . 62 164 A.3.2. Bandwidth Allocation . . . . . . . . . . . . . . . . 62 165 A.4. Candidate Gathering . . . . . . . . . . . . . . . . . . . 62 166 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 63 168 1. Introduction 170 When multimedia communications are established, each 5-tuple reserved 171 for an individual media stream consume additional resources 172 (especially when Interactive Connectivity Establishment (ICE) 173 [RFC5245] is used). For this reason, it is attractive to use a 174 5-tuple for multiple media streams. 176 This specification defines a way to use a single address:port 177 combination (BUNDLE address) for receiving media specified by 178 multiple SDP media descriptions ("m=" lines). 180 This specification defines a new SDP Grouping Framework [RFC5888] 181 extension called 'BUNDLE'. The extension can be used with the 182 Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264] 183 to negotiate the usage of a BUNDLE group. Within the BUNDLE group, a 184 BUNDLE address is used for receiving media specified by multiple "m=" 185 lines. This is referred to as bundled media. 187 The offerer and answerer [RFC3264] use the BUNDLE extension to 188 negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE 189 address) and one for the answerer (answerer BUNDLE address), to be 190 used for receiving the bundled media specified by a BUNDLE group. 191 Once the offerer and the answerer have negotiated a BUNDLE group, 192 they associate their respective BUNDLE address with each "m=" line in 193 the BUNDLE group. The BUNDLE addresses are used to receive all media 194 specified by the BUNDLE group. 196 The use of a BUNDLE group and a BUNDLE address also allows the usage 197 of a single set of Interactive Connectivity Establishment (ICE) 198 [RFC5245] candidates for multiple "m=" lines. 200 This specification also defines a new SDP attribute, 'bundle-only', 201 which can be used to request that specific media is only used if kept 202 within a BUNDLE group. The specification also updates RFC 3264, to 203 allow usage of zero port values without meaning that media is 204 rejected. 206 As defined in RFC 4566 [RFC4566], the semantics of assigning the same 207 transport address (IP address and port) to multiple "m=" lines are 208 undefined, and there is no grouping defined by such means. Instead, 209 an explicit grouping mechanism needs to be used to express the 210 intended semantics. This specification provides such an extension. 212 This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 213 [RFC3264]. The update allows an answerer to assign a non-zero port 214 value to an "m=" line in an SDP answer, even if the "m=" line in the 215 associated SDP offer contained a zero port value. 217 This specification also defines a new Real-time Transport Protocol 218 (RTP) [RFC3550] source description (SDES) item, 'MID', and a new RTP 219 SDES header extension that can be used to associate RTP streams with 220 media descriptions. 222 SDP bodies can contain multiple BUNDLE groups. A given BUNDLE 223 address MUST only be associated with a single BUNDLE group. The 224 procedures in this specification apply independently to a given 225 BUNDLE group. All RTP based media flows described by a single BUNDLE 226 group belong to a single RTP session [RFC3550]. 228 The BUNDLE extension is backward compatible. Endpoints that do not 229 support the extension are expected to generate offers and answers 230 without an SDP 'group:BUNDLE' attribute, and are expected to 231 associate a unique address with each "m=" line within an offer and 232 answer, according to the procedures in [RFC4566] and [RFC3264] 234 2. Terminology 236 "m=" line: SDP bodies contain one or more media descriptions. Each 237 media description is identified by an SDP "m=" line. 239 5-tuple: A collection of the following values: source address, source 240 port, destination address, destination port, and transport-layer 241 protocol. 243 Unique address: An IP address and port combination that is associated 244 with only one "m=" line in an offer or answer. 246 Shared address: An IP address and port combination that is associated 247 with multiple "m=" lines within an offer or answer. 249 Offerer BUNDLE-tag: The first identification-tag in a given SDP 250 'group:BUNDLE' attribute identification-tag list in an offer. 252 Answerer BUNDLE-tag: The first identification-tag in a given SDP 253 'group:BUNDLE' attribute identification-tag list in an answer. 255 Offerer BUNDLE address: Within a given BUNDLE group, an IP address 256 and port combination used by an offerer to receive all media 257 specified by each "m=" line within the BUNDLE group. 259 Answerer BUNDLE address: Within a given BUNDLE group, an IP address 260 and port combination used by an answerer to receive all media 261 specified by each "m=" line within the BUNDLE group. 263 BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer 264 exchange, which uses the same BUNDLE address for receiving media. 266 Bundled "m=" line: An "m=" line, whose identification-tag is placed 267 in an SDP 'group:BUNDLE' attribute identification-tag list in an 268 offer or answer. 270 Bundle-only "m=" line: A bundled "m=" line with an associated SDP 271 'bundle-only' attribute. 273 Bundled media: All media specified by a given BUNDLE group. 275 Initial offer: The first offer, within an SDP session (e.g. a SIP 276 dialog when the Session Initiation Protocol (SIP) [RFC3261] is used 277 to carry SDP), in which the offerer indicates that it wants to create 278 a given BUNDLE group. 280 Subsequent offer: An offer which contains a BUNDLE group that has 281 been created as part of a previous offer/answer exchange. 283 Identification-tag: A unique token value that is used to identify an 284 "m=" line. The SDP 'mid' attribute [RFC5888], associated with an 285 "m=" line, carries an unique identification-tag. The session-level 286 SDP 'group' attribute [RFC5888] carries a list of identification- 287 tags, identifying the "m=" lines associated with that particular 288 'group' attribute. 290 3. Conventions 292 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 293 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 294 document are to be interpreted as described in BCP 14, RFC 2119 295 [RFC2119]. 297 4. Applicability Statement 299 The mechanism in this specification only applies to the Session 300 Description Protocol (SDP) [RFC4566], when used together with the SDP 301 offer/answer mechanism [RFC3264]. Declarative usage of SDP is out of 302 scope of this document, and is thus undefined. 304 5. SDP Grouping Framework BUNDLE Extension 306 This section defines a new SDP Grouping Framework extension 307 [RFC5888], 'BUNDLE'. The BUNDLE extension can be used with the SDP 308 Offer/Answer mechanism to negotiate the usage of a single 309 address:port combination (BUNDLE address) for receiving bundled 310 media. 312 A single address:port combination is also used for sending bundled 313 media. The address:port combination used for sending bundled media 314 MAY be the same as the BUNDLE address, used to receive bundled media, 315 depending on whether symmetric RTP [RFC4961] is used. 317 All media associated with a BUNDLE group MUST be transport using the 318 same transport-layer protocol (e.g., UDP or TCP). 320 The BUNDLE extension is indicated using an SDP 'group' attribute with 321 a "BUNDLE" semantics value [RFC5888]. An identification-tag is 322 associated with each bundled "m=" line, and each identification-tag 323 is listed in the SDP 'group:BUNDLE' attribute identification-tag 324 list. Each "m=" line whose identification-tag is listed in the 325 identification-tag list is associated with a given BUNDLE group. 327 SDP bodies can contain multiple BUNDLE groups. Any given bundled 328 "m=" line MUST NOT be associated with more than one BUNDLE group. 330 NOTE: The order of the "m=" lines listed in the SDP 'group:BUNDLE' 331 attribute identification-tag list does not have to be the same as the 332 order in which the "m=" lines occur in the SDP. 334 Section 8 defines the detailed SDP Offer/Answer procedures for the 335 BUNDLE extension. 337 6. SDP 'bundle-only' Attribute 339 This section defines a new SDP media-level attribute [RFC4566], 340 'bundle-only'. 'bundle-only' is a property attribute [RFC4566], and 341 hence has no value. 343 Name: bundle-only 345 Value: N/A 347 Usage Level: media 349 Charset Dependent: no 351 Example: 353 a=bundle-only 355 In order to ensure that an answerer that does not support the BUNDLE 356 extension always rejects a bundled "m=" line, the offerer can assign 357 a zero port value to the "m=" line. According to [RFC3264] an 358 answerer will reject such "m=" line. By associating an SDP 'bundle- 359 only' attribute with such "m=" line, the offerer can request that the 360 answerer accepts the "m=" line if the answerer supports the Bundle 361 extension, and if the answerer keeps the "m=" line within the 362 associated BUNDLE group. 364 NOTE: Once the offerer BUNDLE address has been selected, the offerer 365 does not need to include the 'bundle-only' attribute in subsequent 366 offers. By associating the offerer BUNDLE address with an "m=" line 367 of a subsequent offer, the offerer will ensure that the answerer will 368 either keep the "m=" line within the BUNDLE group, or the answerer 369 will have to reject the "m=" line. 371 The usage of the 'bundle-only' attribute is only defined for a 372 bundled "m=" line with a zero port value, within an offer. Other 373 usage is unspecified. 375 Section 8 defines the detailed SDP Offer/Answer procedures for the 376 'bundle-only' attribute. 378 7. SDP Information Considerations 380 This section describes restrictions associated with the usage of SDP 381 parameters within a BUNDLE group. It also describes, when parameter 382 and attribute values have been associated with each bundled "m=" 383 line, how to calculate a value for the whole BUNDLE group. 385 7.1. Connection Data (c=) 387 The "c=" line nettype value [RFC4566] associated with a bundled "m=" 388 line MUST be 'IN'. 390 The "c=" line addrtype value [RFC4566] associated with a bundled "m=" 391 line MUST be 'IP4' or 'IP6'. The same value MUST be associated with 392 each "m=" line. 394 NOTE: Extensions to this specification can specify usage of the 395 BUNDLE mechanism for other nettype and addrtype values than the ones 396 listed above. 398 7.2. Bandwidth (b=) 400 An offerer and answerer MUST use the rules and restrictions defined 401 in [I-D.ietf-mmusic-sdp-mux-attributes] for associating the SDP 402 bandwidth (b=) line with bundled "m=" lines. 404 8. SDP Offer/Answer Procedures 406 This section describes the SDP Offer/Answer [RFC3264] procedures for: 408 o Negotiating and creating a BUNDLE group; and 410 o Selecting the BUNDLE addresses (offerer BUNDLE address and 411 answerer BUNDLE address); and 413 o Adding an "m=" line to a BUNDLE group; and 415 o Moving an "m=" line out of a BUNDLE group; and 417 o Disabling an "m=" line within a BUNDLE group. 419 The generic rules and procedures defined in [RFC3264] and [RFC5888] 420 also apply to the BUNDLE extension. For example, if an offer is 421 rejected by the answerer, the previously negotiated SDP parameters 422 and characteristics (including those associated with a BUNDLE group) 423 apply. Hence, if an offerer generates an offer in which the offerer 424 wants to create a BUNDLE group, and the answerer rejects the offer, 425 the BUNDLE group is not created. 427 The procedures in this section are independent of the media type or 428 "m=" line proto value represented by a bundled "m=" line. Section 10 429 defines additional considerations for RTP based media. Section 6 430 defines additional considerations for the usage of the SDP 'bundle- 431 only' attribute. Section 11 defines additional considerations for 432 the usage of Interactive Connectivity Establishment (ICE) 433 [I-D.ietf-ice-rfc5245bis] mechanism. 435 SDP offers and answers can contain multiple BUNDLE groups. The 436 procedures in this section apply independently to a given BUNDLE 437 group. 439 8.1. Mux Category Considerations 441 When an offerer or answerer associates SDP attributes with a bundled 442 "m=" line (including any bundle-only "m=" line) associated with a 443 shared address, IDENTICAL and TRANSPORT mux category SDP attributes 444 [I-D.ietf-mmusic-sdp-mux-attributes] are associated with the "m=" 445 line only if the "m=" line is also associated with the offerer/ 446 answerer BUNDLE-tag. Otherwise the offerer/answerer MUST NOT 447 associate such SDP attributes with the "m=" line. The rule above 448 does not apply to a bundled "m=" line associated with a unique 449 address. 451 NOTE: As bundled "m=" lines (including any bundle-only "m=" line) 452 associated with a shared address will share the same IDENTICAL and 453 TRANSPORT mux category SDP attributes, and attribute values, there is 454 no need to associate such SDP attributes with each "m=" line. The 455 attributes and attribute values are implicitly applied to each "m=" 456 line. 458 The semantics of some SDP attributes only apply to specific types of 459 media. For example, the semantics of the SDP 'rtcp-mux' and SDP 460 'rtcp-mux-only' attributes only apply to "m=" lines describing RTP- 461 based media. However, as described in Section 8.1, there are cases 462 where IDENTICAL and TRANSPORT mux category SDP attributes are only 463 associated with the "m=" line associated with the BUNDLE-tag. That 464 means that media-specific IDENTICAL and TRANSPORT mux category 465 attributes can be associated with an "m=" line associated with 466 another type of media. 468 8.2. Generating the Initial SDP Offer 470 When an offerer generates an initial offer, in order to create a 471 BUNDLE group, it MUST: 473 o Assign a unique address to each "m=" line within the offer, 474 following the procedures in [RFC3264], unless the media line is a 475 'bundle-only' "m=" line (see below); and 477 o Add an SDP 'group:BUNDLE' attribute to the offer; and 479 o Place the identification-tag of each bundled "m=" line in the SDP 480 'group:BUNDLE' attribute identification-tag list; and 482 o Indicate which unique address the offerer suggests as the offerer 483 BUNDLE address [Section 8.2.1]. 485 If the offerer wants to request that the answerer accepts a given 486 bundled "m=" line only if the answerer keeps the "m=" line within the 487 BUNDLE group, the offerer MUST: 489 o Associate an SDP 'bundle-only' attribute [Section 8.2.1] with the 490 "m=" line; and 492 o Assign a zero port value to the "m=" line. 494 NOTE: If the offerer assigns a zero port value to an "m=" line, but 495 does not also associate an SDP 'bundle-only' attribute with the "m=" 496 line, it is an indication that the offerer wants to disable the "m=" 497 line [Section 8.5.4]. 499 [Section 18.1] shows an example of an initial offer. 501 8.2.1. Suggesting the offerer BUNDLE address 503 In the offer, the address associated with the "m=" line associated 504 with the offerer BUNDLE-tag indicates the address that the offerer 505 suggests as the offerer BUNDLE address. 507 The "m=" line associated with the offerer BUNDLE-tag MUST NOT contain 508 a zero port value or an SDP 'bundle-only' attribute. 510 8.2.2. Example: Initial SDP Offer 512 The example shows an initial SDP offer. The offer includes two "m=" 513 lines in the SDP, and suggests that both are included in a BUNDLE 514 group. The audio "m=" line is associated with the offerer BUNDLE-tag 515 (placed first in the SDP group:BUNDLE attribute identificatoin-id 516 list). 518 SDP Offer 520 v=0 521 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 522 s= 523 c=IN IP4 atlanta.example.com 524 t=0 0 525 a=group:BUNDLE foo bar 526 m=audio 10000 RTP/AVP 0 8 97 527 b=AS:200 528 a=mid:foo 529 a=rtcp-mux 530 a=rtpmap:0 PCMU/8000 531 a=rtpmap:8 PCMA/8000 532 a=rtpmap:97 iLBC/8000 533 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 534 m=video 10002 RTP/AVP 31 32 535 b=AS:1000 536 a=mid:bar 537 a=rtpmap:31 H261/90000 538 a=rtpmap:32 MPV/90000 539 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 541 8.3. Generating the SDP Answer 543 When an answerer generates an answer that contains a BUNDLE group, 544 the following general SDP grouping framework restrictions, defined in 545 [RFC5888], also apply to the BUNDLE group: 547 o The answerer MUST NOT include a BUNDLE group in the answer, unless 548 the offerer requested the BUNDLE group to be created in the 549 corresponding offer; and 551 o The answerer MUST NOT include an "m=" line within a BUNDLE group, 552 unless the offerer requested the "m=" line to be within that 553 BUNDLE group in the corresponding offer. 555 If the answer contains a BUNDLE group, the answerer MUST: 557 o Select an Offerer BUNDLE Address [Section 8.3.1]; and 559 o Select an Answerer BUNDLE Address [Section 8.3.2]; 561 The answerer is allowed to select a new Answerer BUNDLE address each 562 time it generates an answer to an offer. 564 If the answerer does not want to keep an "m=" line within a BUNDLE 565 group, it MUST: 567 o Move the "m=" line out of the BUNDLE group [Section 8.3.3]; or 569 o Reject the "m=" line [Section 8.3.4]; 571 If the answerer keeps a bundle-only "m=" line within the BUNDLE 572 group, it follows the procedures (associates the answerer BUNDLE 573 address with the "m=" line etc) for any other "m=" line kept within 574 the BUNDLE group. 576 If the answerer does not want to keep a bundle-only "m=" line within 577 the BUNDLE group, it MUST reject the "m=" line [Section 8.3.4]. 579 The answerer MUST NOT associate an SDP 'bundle-only' attribute with 580 any "m=" line in an answer. 582 NOTE: If a bundled "m=" line in an offer contains a zero port value, 583 but the "m=" line does not contain an SDP 'bundle-only' attribute, it 584 is an indication that the offerer wants to disable the "m=" line 585 [Section 8.5.4]. 587 8.3.1. Answerer Selection of Offerer Bundle Address 589 In an offer, the address (unique or shared) associated with the 590 bundled "m=" line associated with the offerer BUNDLE-tag indicates 591 the address that the offerer suggests as the offerer BUNDLE address 592 [Section 8.2.1]. The answerer MUST check whether that "m=" line 593 fulfils the following criteria: 595 o The answerer will not move the "m=" line out of the BUNDLE group 596 [Section 8.3.3]; and 598 o The answerer will not reject the "m=" line [Section 8.3.4]; and 600 o The "m=" line does not contain a zero port value. 602 If all of the criteria above are fulfilled, the answerer MUST select 603 the address associated with the "m=" line as the offerer BUNDLE 604 address. In the answer, the answerer BUNDLE-tag represents the "m=" 605 line, and the address associated with the "m=" line in the offer 606 becomes the offerer BUNDLE address. 608 If one or more of the criteria are not fulfilled, the answerer MUST 609 select the next identification-tag in the identification-tag list, 610 and perform the same criteria check for the "m=" line associated with 611 that identification-tag. If there are no more identification-tags in 612 the identification-tag list, the answerer MUST NOT create the BUNDLE 613 group. In addition, unless the answerer rejects the whole offer, the 614 answerer MUST apply the answerer procedures for moving an "m=" line 615 out of a BUNDLE group [Section 8.3.3] to each bundled "m=" line in 616 the offer when creating the answer. 618 [Section 18.1] shows an example of an offerer BUNDLE address 619 selection. 621 8.3.2. Answerer Selection of Answerer BUNDLE Address 623 When the answerer selects a BUNDLE address for itself, referred to as 624 the answerer BUNDLE address, it MUST associate that address with each 625 bundled "m=" line within the created BUNDLE group in the answer. 627 The answerer MUST NOT associate the answerer BUNDLE address with an 628 "m=" line that is not within the BUNDLE group, or to an "m=" line 629 that is within another BUNDLE group. 631 [Section 18.1] shows an example of an answerer BUNDLE address 632 selection. 634 8.3.3. Moving A Media Description Out Of A BUNDLE Group 636 When an answerer wants to move an "m=" line out of a BUNDLE group, it 637 MUST first check the following criteria: 639 o In the corresponding offer, the "m=" line is associated with a 640 shared address (e.g. a previously selected offerer BUNDLE 641 address); or 643 o In the corresponding offer, an SDP 'bundle-only' attribute is 644 associated with the "m=" line, and the "m=" line contains a zero 645 port value. 647 If either criteria above is fulfilled, the answerer MUST reject the 648 "m=" line [Section 8.3.4]. 650 Otherwise, if in the corresponding offer the "m=" line is associated 651 with a unique address, the answerer MUST associate a unique address 652 with the "m=" line in the answer (the answerer does not reject the 653 "m=" line). 655 In addition, in either case above, the answerer MUST NOT place the 656 identification-tag, associated with the moved "m=" line, in the SDP 657 'group' attribute identification-tag list associated with the BUNDLE 658 group. 660 8.3.4. Rejecting A Media Description In A BUNDLE Group 662 When an answerer rejects an "m=" line, it MUST associate an address 663 with a zero port value with the "m=" line in the answer, according to 664 the procedures in [RFC3264]. 666 In addition, the answerer MUST NOT place the identification-tag, 667 associated with the rejected "m=" line, in the SDP 'group' attribute 668 identification-tag list associated with the BUNDLE group. 670 8.3.5. Example: SDP Answer 672 The example shows an SDP answer, based on the SDP offer in 673 [Section 8.2.2]. The answers acceppts both "m=" lines in the BUNDLE 674 group. 676 SDP Answer 678 v=0 679 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 680 s= 681 c=IN IP4 biloxi.example.com 682 t=0 0 683 a=group:BUNDLE foo bar 684 m=audio 20000 RTP/AVP 0 685 b=AS:200 686 a=mid:foo 687 a=rtcp-mux 688 a=rtpmap:0 PCMU/8000 689 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 690 m=video 20000 RTP/AVP 32 691 b=AS:1000 692 a=mid:bar 693 a=rtpmap:32 MPV/90000 694 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 696 8.4. Offerer Processing of the SDP Answer 698 When an offerer receives an answer, if the answer contains a BUNDLE 699 group, the offerer MUST check that any bundled "m=" line in the 700 answer was indicated as bundled in the corresponding offer. If there 701 is no mismatch, the offerer MUST use the offerer BUNDLE address, 702 selected by the answerer [Section 8.3.1], as the address for each 703 bundled "m=" line. 705 NOTE: As the answerer might reject one or more bundled "m=" lines, or 706 move a bundled "m=" line out of a BUNDLE group, each bundled "m=" 707 line in the offer might not be indicated as bundled in the answer. 709 If the answer does not contain a BUNDLE group, the offerer MUST 710 process the answer as a normal answer. 712 8.5. Modifying the Session 714 When an offerer generates a subsequent offer, it MUST associate the 715 previously selected offerer BUNDLE address [Section 8.3.1] with each 716 bundled "m=" line (including any bundle-only "m=" line), except if: 718 o The offerer suggests a new offerer BUNDLE address [Section 8.5.1]; 719 or 721 o The offerer wants to add a bundled "m=" line to the BUNDLE group 722 [Section 8.5.2]; or 724 o The offerer wants to move a bundled "m=" line out of the BUNDLE 725 group [Section 8.5.3]; or 727 o The offerer wants to disable the bundled "m=" line 728 [Section 8.5.4]. 730 In addition, the offerer MUST select an offerer BUNDLE-tag 731 [Section 8.2.1] associated with the previously selected offerer 732 BUNDLE address, unless the offerer suggests a new offerer BUNDLE 733 address. 735 8.5.1. Suggesting a new offerer BUNDLE address 737 When an offerer generates an offer, in which it suggests a new 738 offerer BUNDLE address [Section 8.2.1], the offerer MUST: 740 o Assign the address (shared address) to each "m=" line within the 741 BUNDLE group; or 743 o Assign the address (unique address) to one bundled "m=" line. 745 In addition, the offerer MUST indicate that the address is the new 746 suggested offerer BUNDLE address [Section 8.2.1]. 748 NOTE: Unless the offerer associates the new suggested offerer BUNDLE 749 address with each bundled "m=" line, it can associate unique 750 addresses with any number of bundled "m=" lines (and the previously 751 selected offerer BUNDLE address to any remaining bundled "m=" line) 752 if it wants to suggest multiple alternatives for the new offerer 753 BUNDLE address. 755 8.5.2. Adding a media description to a BUNDLE group 757 When an offerer generates an offer, in which it wants to add a 758 bundled "m=" line to a BUNDLE group, the offerer MUST: 760 o Assign a unique address to the added "m=" line; or 762 o Assign the previously selected offerer BUNDLE address to the added 763 "m=" line; or 765 o If the offerer associates a new (shared address) suggested offerer 766 BUNDLE address with each bundled "m=" line [Section 8.5.1], also 767 associate that address with the added "m=" line. 769 In addition, the offerer MUST add the identification-tag associated 770 with the added "m=" line to the SDP 'group:BUNDLE' attribute 771 identification-tag list with the BUNDLE group [Section 8.2.1]. 773 NOTE: Assigning a unique address to the "m=" line allows the answerer 774 to move the "m=" line out of the BUNDLE group [Section 8.3.3], 775 without having to reject the "m=" line. 777 If the offerer associates a unique address with the added "m=" line, 778 and if the offerer suggests that address as the new offerer BUNDLE 779 address [Section 8.5.1], the offerer BUNDLE-tag MUST represent the 780 added "m=" line [Section 8.2.1]. 782 If the offerer associates a new suggested offerer BUNDLE address with 783 each bundled "m=" line [Section 8.5.1], including the added "m=" 784 line, the offerer BUNDLE-tag MAY represent the added "m=" line 785 [Section 8.2.1]. 787 [Section 18.3] shows an example where an offerer sends an offer in 788 order to add a bundled "m=" line to a BUNDLE group. 790 8.5.3. Moving A Media Description Out Of A BUNDLE Group 792 When an offerer generates an offer, in which it wants to move a 793 bundled "m=" line out of a BUNDLE group it was added to in a previous 794 offer/answer transaction, the offerer: 796 o MUST associate a unique address with the "m=" line; and 797 o MUST NOT place the identification-tag associated with the "m=" 798 line in the SDP 'group:BUNDLE' attribute identification-tag list 799 associated with the BUNDLE group. 801 NOTE: If the removed "m=" line is associated with the previously 802 selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag 803 [Section 8.2.1]. 805 NOTE: If an "m=" line, when being moved out of a BUNDLE group, is 806 added to another BUNDLE group, the offerer applies the procedures in 807 [Section 8.5.2] to the "m=" line. 809 [Section 18.4] shows an example of an offer for moving an "m=" line 810 out of a BUNDLE group. 812 8.5.4. Disabling A Media Description In A BUNDLE Group 814 When an offerer generates an offer, in which it wants to disable a 815 bundled "m=" line (added to the BUNDLE group in a previous offer/ 816 answer transaction), the offerer: 818 o MUST associate an address with a zero port value with the "m=" 819 line, following the procedures in [RFC4566]; and 821 o MUST NOT place the identification-tag associated with the "m=" 822 line in the SDP 'group:BUNDLE' attribute identification-tag list 823 associated with the BUNDLE group. 825 [Section 18.5] shows an example of an offer for disabling an "m=" 826 line within a BUNDLE group. 828 9. Protocol Identification 830 Each "m=" line within a BUNDLE group MUST use the same transport- 831 layer protocol. If bundled "m=" lines use different protocols on top 832 of the transport-layer protocol, there MUST exist a publicly 833 available specification which describes a mechanism, for this 834 particular protocol combination, how to associate received data with 835 the correct protocol. 837 In addition, if received data can be associated with more than one 838 bundled "m=" line, there MUST exist a publicly available 839 specification which describes a mechanism for associating the 840 received data with the correct "m=" line. 842 This document describes a mechanism to identify the protocol of 843 received data among the STUN, DTLS and SRTP protocols (in any 844 combination), when UDP is used as transport-layer protocol, but does 845 not describe how to identify different protocols transported on DTLS. 846 While the mechanism is generally applicable to other protocols and 847 transport-layer protocols, any such use requires further 848 specification around how to multiplex multiple protocols on a given 849 transport-layer protocol, and how to associate received data with the 850 correct protocols. 852 9.1. STUN, DTLS, SRTP 854 Section 5.1.2 of [RFC5764] describes a mechanism to identify the 855 protocol of a received packet among the STUN, Datagram Transport 856 Layer Security (DTLS) and SRTP protocols (in any combination). If an 857 offer or answer includes bundled "m=" lines that represent these 858 protocols, the offerer or answerer MUST support the mechanism 859 described in [RFC5764], and no explicit negotiation is required in 860 order to indicate support and usage of the mechanism. 862 [RFC5764] does not describe how to identify different protocols 863 transported on DTLS, only how to identify the DTLS protocol itself. 864 If multiple protocols are transported on DTLS, there MUST exist a 865 specification describing a mechanism for identifying each individual 866 protocol. In addition, if a received DTLS packet can be associated 867 with more than one "m=" line, there MUST exist a specification which 868 describes a mechanism for associating the received DTLS packet with 869 the correct "m=" line. 871 [Section 10.2] describes how to associate the packets in a received 872 SRTP stream with the correct "m=" line. 874 10. RTP Considerations 876 10.1. Single RTP Session 878 All RTP-based media within a single BUNDLE group belong to a single 879 RTP session [RFC3550]. 881 Since a single RTP session is used for each bundle group, all "m=" 882 lines representing RTP-based media in a bundle group will share a 883 single SSRC numbering space [RFC3550]. 885 The following rules and restrictions apply for a single RTP session: 887 o A specific payload type value can be used in multiple bundled "m=" 888 lines only if each codec associated with the payload type number 889 shares an identical codec configuration [Section 10.1.1]. 891 o The proto value in each bundled RTP-based "m=" line MUST be 892 identical (e.g. RTP/AVPF). 894 o The RTP MID header extension MUST be enabled, by associating an 895 SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp- 896 hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line 897 in every offer and answer. 899 o A given SSRC MUST NOT transmit RTP packets using payload types 900 that originate from different bundled "m=" lines. 902 NOTE: The last bullet above is to avoid sending multiple media types 903 from the same SSRC. If transmission of multiple media types are done 904 with time overlap, RTP and RTCP fail to function. Even if done in 905 proper sequence this causes RTP Timestamp rate switching issues 906 [RFC7160]. However, once an SSRC has left the RTP session (by 907 sending an RTCP BYE packet), that SSRC can be reused by another 908 source (possibly associated with a different bundled "m=" line) after 909 a delay of 5 RTCP reporting intervals (the delay is to ensure the 910 SSRC has timed out, in case the RTCP BYE packet was lost [RFC3550]). 912 10.1.1. Payload Type (PT) Value Reuse 914 Multiple bundled "m=" lines might represent RTP based media. As all 915 RTP based media specified by a BUNDLE group belong to the same RTP 916 session, in order for a given payload type value to be used inside 917 more than one bundled "m=" line, all codecs associated with the 918 payload type number MUST share an identical codec configuration. 919 This means that the codecs MUST share the same media type, encoding 920 name, clock rate and any parameter that can affect the codec 921 configuration and packetization. 922 [I-D.ietf-mmusic-sdp-mux-attributes] lists SDP attributes, whose 923 attribute values must be identical for all codecs that use the same 924 payload type value. 926 10.2. Associating RTP/RTCP Streams With Correct SDP Media Description 928 NOTE: The text in this section is copied from Appendix B of JSEP. 929 The community has not yet agreed on the text. 931 As described in [RFC3550], RTP packets are associated with RTP 932 streams [RFC7656]. Each RTP stream is identified by an SSRC value, 933 and each RTP packet includes an SSRC field that is used to associate 934 the packet with the correct RTP stream. RTCP packets also use SSRCs 935 to identify which RTP streams the packet relates to. However, a RTCP 936 packet can contain multiple SSRC fields, in the course of providing 937 feedback or reports on different RTP streams, and therefore can be 938 associated with multiple such streams. 940 In order to be able to process received RTP/RTCP packets correctly, 941 it must be possible to associate an RTP stream with the correct "m=" 942 line, as the "m=" line and SDP attributes associated with the "m=" 943 line contain information needed to process the packets. 945 As all RTP streams associated with a BUNDLE group use the same 946 address:port combination for sending and receiving RTP/RTCP packets, 947 the local address:port combination cannot be used to associate an RTP 948 stream with the correct "m=" line. In addition, multiple RTP streams 949 might be associated with the same "m=" line. 951 An offerer and answerer can inform each other which SSRC values they 952 will use for an RTP stream by using the SDP 'ssrc' attribute 953 [RFC5576]. However, an offerer will not know which SSRC values the 954 answerer will use until the offerer has received the answer providing 955 that information. Due to this, before the offerer has received the 956 answer, the offerer will not be able to associate an RTP stream with 957 the correct "m=" line using the SSRC value associated with the RTP 958 stream. In addition, the offerer and answerer may start using new 959 SSRC values mid-session, without informing each other using the SDP 960 'ssrc' attribute. 962 In order for an offerer and answerer to always be able to associate 963 an RTP stream with the correct "m=" line, the offerer and answerer 964 using the BUNDLE extension MUST support the mechanism defined in 965 Section 15, where the offerer and answerer insert the identification- 966 tag associated with an "m=" line (provided by the remote peer) into 967 RTP and RTCP packets associated with a BUNDLE group. 969 When using this mechanism, the mapping from an SSRC to an 970 identification-tag is carried in RTP header extensions or RTCP SDES 971 packets, as specified in Section 15. Since a compound RTCP packet 972 can contain multiple RTCP SDES packets, and each RTCP SDES packet can 973 contain multiple chunks, a single RTCP packet can contain several 974 SSRC to identification-tag mappings. The offerer and answerer 975 maintain tables used for routing that are updated each time an RTP/ 976 RTCP packet contains new information that affects how packets should 977 be routed. 979 However, some implementations of may not include this identification- 980 tag in their RTP and RTCP traffic when using the BUNDLE mechanism, 981 and instead use a payload type based mechanism to associate RTP 982 streams with SDP m= lines. In this situation, each "m=" line MUST 983 use unique payload type values, in order for the payload type to be a 984 reliable indicator of the relevant "m=" line for the RTP stream. 985 Note that when using the payload type to associate RTP streams with 986 m= lines an RTP stream, identified by SSRC, will be mapped to an "m=" 987 line when the first packet of that RTP stream is received, and the 988 mapping will not be changed even if the payload type used by that RTP 989 stream changes. In other words, the SSRC cannot to "move" to a 990 different "m=" line simply by changing the payload type. 992 Applications can implement RTP stacks in many different ways. The 993 algorithm below details one way that RTP streams can be associated 994 with m= lines, but is not meant to be prescriptive about exactly how 995 an RTP stack needs to be implemented. Applications MAY use any 996 algorithm that achieves equivalent results to those described in the 997 algorithm below. 999 To prepare to associate RTP streams with the correct "m=" line, the 1000 following steps MUST be followed for each BUNDLE group. 1002 Construct a table mapping MID to "m=" line for each "m=" line in 1003 this BUNDLE group. Note that an "m=" line may only have one MID. 1005 Construct a table mapping SSRCs of incoming RTP streams to "m=" 1006 line for each "m=" line in this BUNDLE group and for each SSRC 1007 configured for receiving in that "m=" line. 1009 Construct a table mapping the SSRC of each outgoing RTP stream to 1010 "m=line" for each "m=" line in this BUNDLE group and for each SSRC 1011 configured for sending in that "m=" line. 1013 Construct a table mapping payload type to "m=" line for each "m=" 1014 line in the BUNDLE group and for each payload type configured for 1015 receiving in that "m=" line. If any payload type is configured 1016 for receiving in more than one "m=" line in the BUNDLE group, do 1017 not it include it in the table, as it cannot be used to uniquely 1018 identify a "m=" line. 1020 Note that for each of these tables, there can only be one mapping 1021 for any given key (MID, SSRC, or PT). In other words, the tables 1022 are not multimaps. 1024 As "m=" lines are added or removed from the BUNDLE groups, or their 1025 configurations are changed, the tables above MUST also be updated. 1027 When an RTP packet is received, it MUST be delivered to the RTP 1028 stream corresponding to its SSRC. That RTP stream MUST then be 1029 associated with the correct m= line within a BUNDLE group, for 1030 additional processing, according to the following steps. 1032 If the MID associated with the RTP stream is not in the table 1033 mapping MID to a€œm=a€œ line, then the RTP 1034 stream is not decoded and the payload data is discarded. 1036 If the packet has a MID, and the packet's extended sequence number 1037 is greater than that of the last MID update, as discussed in 1038 [RFC7941], Section 4.2.6, update the MID associated with the RTP 1039 stream to match the MID carried in the RTP packet, then update the 1040 mapping tables to include an entry that maps the SSRC of that RTP 1041 stream to the a€œm=a€œ line for that MID. 1043 If the SSRC of the RTP stream is in the incoming SSRC mapping 1044 table, check that the payload type used by the RTP stream matches 1045 a payload type included on the matching 1046 a€œm=a€œ line. If so, associate the RTP 1047 stream with that a€œm=a€œ line. Otherwise, 1048 the RTP stream is not decoded and the payload data is discarded. 1050 If the payload type used by the RTP stream is in the payload type 1051 table, update the incoming SSRC mapping table to include an entry 1052 that maps the RTP streama€™s SSRC to the 1053 a€œm=a€œ line for that payload type. 1054 Associate the RTP stream with the corresponding 1055 a€œm=a€œ line. 1057 Otherwise, mark the RTP stream as not for decoding and discard the 1058 payload. 1060 If the RTP packet contains one of more contributing source (CSRC) 1061 identifiers, then each CSRC is looked up in the incoming SSRC table 1062 and a copy of the RTP packet is associated with the corresponding m= 1063 line for additional processing. 1065 For each RTCP packet received (including each RTCP packet that is 1066 part of a compound RTCP packet), the packet is processed as usual by 1067 the RTP layer, then is passed to the a€œm=a€œ 1068 lines corresponding to the RTP streams it contains information about 1069 for additional processing. This routing is type-dependent, as each 1070 kind of RTCP packet has its own mechanism for associating it with the 1071 relevant RTP streams. 1073 RTCP packets for which no appropriate a€œm=a€œ 1074 line can be identified MUST be processed as usual by the RTP layer, 1075 updating the metadata associated with the corresponding RTP streams, 1076 but are not passed to any a€œm=a€œ line. This 1077 situation can occur with certain multiparty RTP topologies, or when 1078 RTCP packets are sent containing a subset of the SDES information. 1080 Rules for additional processing of the various types of RTCP packets 1081 are explained below. 1083 If the RTCP packet is of type SDES, for each chunk in the packet 1084 whose SSRC is found in the incoming SSRC table, deliver a copy of 1085 the SDES packet to the "m=" line associated with that SSRC. In 1086 addition, for any SDES MID items contained in these chunks, if the 1087 MID is found in the table mapping MID to "m=" line, update the 1088 incoming SSRC table to include an entry that maps the RTP stream 1089 associated with chunk's SSRC to the "m=" line associated with that 1090 MID, unless the packet is older than the packet that most recently 1091 updated the mapping for this SSRC, as discussed in [RFC7941], 1092 Section 4.2.6. 1094 Note that if an SDES packet is received as part of a compound RTCP 1095 packet, the SSRC to "m=" line mapping may not exist until the SDES 1096 packet is handled (e.g., in the case where RTCP for a source is 1097 received before any RTP packets). Therefore, when processing a 1098 compound packet, any contained SDES packet MUST be handled first. 1099 Note that this is a backwards change from [RFC3550] Section 6.1, 1100 which states that "Each individual RTCP packet in the compound 1101 packet may be processed independently with no requirements upon 1102 the order or combination of packets". 1104 If the RTCP packet is of type BYE, it indicates that the RTP 1105 streams referenced in the packet are ending. Therefore, for each 1106 SSRC indicated in the packet that is found in the incoming SSRC 1107 table, first deliver a copy of the BYE packet to the "m=" line 1108 associated with that SSRC, but then remove the entry for that SSRC 1109 from the incoming SSRC table after an appropriate delay to account 1110 for "straggler packets", as specified in [RFC3550], Section 6.2.1. 1112 If the RTCP packet is of type SR or RR, for each report block in 1113 the report whose "SSRC of source" is found in the outgoing SSRC 1114 table, deliver a copy of the SR or RR packet to the "m=" line 1115 associated with that SSRC. In addition, if the packet is of type 1116 SR, and the sender SSRC for the packet is found in the incoming 1117 SSRC table, deliver a copy of the SR packet to the "m=" line 1118 associated with that SSRC. 1120 If the implementation supports RTCP XR and the packet is of type 1121 XR, as defined in [RFC3611], for each report block in the report 1122 whose "SSRC of source" is is found in the outgoing SSRC table, 1123 deliver a copy of the XR packet to the "m=" line associated with 1124 that SSRC. In addition, if the sender SSRC for the packet is 1125 found in the incoming SSRC table, deliver a copy of the XR packet 1126 to the "m=" line associated with that SSRC. 1128 If the RTCP packet is a feedback message of type RTPFB or PSFB, as 1129 defined in [RFC4585], it will contain a media source SSRC, and 1130 this SSRC is used for routing certain subtypes of feedback 1131 messages. However, several subtypes of PSFB messages include 1132 target SSRC(s) in a section called Feedback Control Information 1133 (FCI). For these messages, the target SSRC(s) are used for 1134 routing. 1136 If the RTCP packet is a feedback packet that does not include 1137 target SSRCs in its FCI section, and the media source SSRC is 1138 found in the outgoing SSRC table, deliver the feedback packet to 1139 the "m=" line associated with that SSRC. RTPFB and PSFB types 1140 that are handled in this way include: 1142 Generic NACK: [RFC4585] (PT=RTPFB, FMT=1). 1144 Picture Loss Indication (PLI): [RFC4585] (PT=PSFB, FMT=1). 1146 Slice Loss Indication (SLI): [RFC4585] (PT=PSFB, FMT=2). 1148 Reference Picture Selection Indication (RPSI): [RFC4585] 1149 (PT=PSFB, FMT=3). 1151 If the RTCP packet is a feedback message that does include target 1152 SSRC(s) in its FCI section, it can either be a request or a 1153 notification. Requests reference a RTP stream that is being sent 1154 by the message recipient, whereas notifications are responses to 1155 an earlier request, and therefore reference a RTP stream that is 1156 being received by the message recipient. 1158 If the RTCP packet is a feedback request that includes target 1159 SSRC(s), for each target SSRC that is found in the outgoing SSRC 1160 table, deliver a copy of the RTCP packet to the "m=" line 1161 associated with that SSRC. PSFB types that are handled in this 1162 way include: 1164 Full Intra Request (FIR): [RFC5104] (PT=PSFB, FMT=4). 1166 Temporal-Spatial Trade-off Request (TSTR): [RFC5104] (PT=PSFB, 1167 FMT=5). 1169 H.271 Video Back Channel Message (VBCM): [RFC5104] (PT=PSFB, 1170 FMT=7). 1172 Layer Refresh Request (LRR): [I-D.ietf-avtext-lrr] (PT=PSFB, 1173 FMT=TBD). 1175 If the RTCP packet is a feedback notification that include target 1176 SSRC(s), for each target SSRC that is found in the incoming SSRC 1177 table, deliver a copy of the RTCP packet to the "m=" line 1178 associated with the RTP stream with matching SSRC. PSFB types 1179 that are handled in this way include: 1181 Temporal-Spatial Trade-off Notification (TSTN): [RFC5104] 1182 (PT=PSFB, FMT=6). This message is a notification in response 1183 to a prior TSTR. 1185 If the RTCP packet is of type APP, then it is handled in an 1186 application specific manner. If the application does not 1187 recognise the APP packet, then it MUST be discarded. 1189 10.3. RTP/RTCP Multiplexing 1191 Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP 1192 multiplexing [RFC5761] for the RTP-based media specified by the 1193 BUNDLE group. 1195 When RTP/RTCP multiplexing is enabled, the same address:port 1196 combination will be used for sending all RTP packets and the RTCP 1197 packets associated with the BUNDLE group. Each endpoint will send 1198 the packets towards the BUNDLE address of the other endpoint. The 1199 same address:port combination MAY be used for receiving RTP packets 1200 and RTCP packets. 1202 10.3.1. SDP Offer/Answer Procedures 1204 This section describes how an offerer and answerer use the SDP 'rtcp- 1205 mux' attribute [RFC5761] and the SDP 'rtcp-mux-only' attribute 1206 [I-D.ietf-mmusic-mux-exclusive] to negotiate usage of RTP/RTCP 1207 multiplexing for RTP-based media associated with a BUNDLE group. 1209 The mux category [I-D.ietf-mmusic-sdp-mux-attributes] of the SDP 1210 'rtcp-mux' and 'rtcp-mux-only' attributes is IDENTICAL. Section 8.1 1211 describes the details regarding which bundled "m=" lines an offerer 1212 and answerer associates the attributes with. 1214 RTP/RTCP multiplexing only applies to RTP-based media. However, as 1215 described in Section 8.1, within a BUNDLE group the SDP 'rtcp-mux' 1216 and SDP 'rtcp-mux-only' attributes might be associated with a non- 1217 RTP-based bundled "m=" line. 1219 10.3.1.1. Generating the Initial SDP Offer 1221 When an offerer generates an initial offer, if the offer contains one 1222 or more RTP-based bundled "m=" lines (or, if there is a chance that 1223 RTP-based "m=" lines will later be added to the BUNDLE group), the 1224 offerer MUST associate an SDP 'rtcp-mux' attribute [RFC5761] with one 1225 or more "m=" lines, following the procedures for IDENTICAL mux 1226 category attributes in Section 8.1. In addition, the offerer MAY 1227 associate an SDP 'rtcp-mux-only' attribute 1228 [I-D.ietf-mmusic-mux-exclusive] with the same "m=" lines. 1230 NOTE: Whether the offerer associates the SDP 'rtcp-mux-only' 1231 attribute depends on whether the offerer supports fallback to usage 1232 of a separate port for RTCP in case the answerer moves one or more 1233 RTP-based "m=" line out of the BUNDLE group in the answer. 1235 NOTE: If the offerer associates an SDP 'rtcp-mux' attribute with one 1236 or more bundled "m=" lines, but does not associate an SDP 'rtcp-mux- 1237 only' attribute, the offerer can also associate an SDP 'rtcp' 1238 attribute [RFC3605] with one or more RTP-based "m=" line in order to 1239 provide a fallback port for RTCP, as described in [RFC5761]. 1240 However, the fallback port will only be used for RTP-based "m=" lines 1241 moved out of the BUNDLE group by the answerer. 1243 In the initial offer, the address:port combination for RTCP MUST be 1244 unique in each bundled RTP-based "m=" line (excluding a bundle-only 1245 "m=" line), similar to RTP. 1247 10.3.1.2. Generating the SDP Answer 1249 When an answerer generates an answer, if the answerer supports RTP- 1250 based media, and if a bundled "m=" line in the offer contained an SDP 1251 'rtcp-mux' attribute, the answerer MUST enable usage of RTP/RTCP 1252 multiplexing, even if there currently are no RTP-based "m=" lines 1253 within the BUNDLE group. The answerer MUST associate an SDP 'rtcp- 1254 mux' attribute with "m=" lines within the BUNDLE group in the answer 1255 following the procedures for IDENTICAL mux category attributes in 1256 Section 8.1. In addition, if the "m=" line in the offer contained an 1257 an SDP "rtcp-mux-only" attribute, the answerer MUST associate an SDP 1258 "rtcp-mux-only" attribute with the "m=" line in the answer. 1260 If the "m=" line associated with the offerer BUNDLE-tag in the offer 1261 contained an SDP 'rtcp-mux-only' attribute, and if the answerer moves 1262 an RTP-based "m=" line out of the BUNDLE group in the answer 1263 Section 8.3.3, the answerer MUST either associate the attribute with 1264 the moved "m=" line (and enable RTP/RTCP multiplexing for the media 1265 associated with the "m=" line), or reject the "m=" line 1266 Section 8.3.4. 1268 The answerer MUST NOT associate an SDP 'rtcp' attribute with any "m=" 1269 line within the BUNDLE group in the answer. The answerer will use 1270 the port value of the selected offerer BUNDLE address for sending RTP 1271 and RTCP packets associated with each RTP-based bundled "m=" line 1272 towards the offerer. 1274 If the usage of RTP/RTCP multiplexing within a BUNDLE group has been 1275 negotiated in a previous offer/answer transaction, the answerer MUST 1276 associate an SDP 'rtcp-mux' attribute with the "m=" line associated 1277 with the answerer BUNDLE-tag in the answer. It is not possible to 1278 disable RTP/RTCP multiplexing within a BUNDLE group. 1280 10.3.1.3. Offerer Processing of the SDP Answer 1282 When an offerer receives an answer, if the answerer has accepted the 1283 usage of RTP/RTCP multiplexing (see Section 10.3.1.2), the answerer 1284 follows the procedures for RTP/RTCP multiplexing defined in 1285 [RFC5761]. The offerer will use the port value associated with the 1286 answerer BUNDLE address for sending RTP and RTCP packets associated 1287 with each RTP-based bundled "m=" line towards the answerer. 1289 NOTE: It is considered a protocol error if the answerer has not 1290 accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines 1291 that the answerer included in the BUNDLE group. 1293 10.3.1.4. Modifying the Session 1295 When an offerer generates a subsequent offer, the offerer MUST 1296 associate an SDP 'rtcp-mux' attribute with a bundled "m=" line, 1297 following the procedures for IDENTICAL mux category attributes in 1298 Section 8.1. 1300 If the offerer wants to add a bundled RTP-based "m=" line to the 1301 BUNDLE group, it MAY also associate an SDP 'rtcp-mux-only' attribute 1302 with a bundled "m=", following the procedures for IDENTICAL mux 1303 category attributes in Section 8.1. This allows the offerer to 1304 mandate RTP/RTCP multiplexing for the added "m=" line (or the "m=" 1305 line to be rejected by the answerer) even if the answerer does not 1306 accept the "m=" line within the BUNDLE group. 1308 11. ICE Considerations 1310 This section describes how to use the BUNDLE grouping extension 1311 together with the Interactive Connectivity Establishment (ICE) 1312 mechanism [I-D.ietf-ice-rfc5245bis]. 1314 The generic procedures for negotiating usage of ICE using SDP, 1315 defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE 1316 with BUNDLE, with the following exceptions: 1318 o When BUNDLE addresses for a BUNDLE group have been selected for 1319 both endpoints, ICE connectivity checks and keep-alives only need 1320 to be performed for the whole BUNDLE group, instead of per bundled 1321 "m=" line. 1323 o Among bundled "m=" lines (including any bundle-only "m=" line) 1324 with which the offerer has associated a shared address, the 1325 offerer only associates ICE-related media-level SDP attributes 1326 with the "m=" line associated with the offerer BUNDLE-tag, 1327 following the procedures in Section 8.1. 1329 o Among "m=" lines with which the answerer has associated a shared 1330 address within a BUNDLE group, the answerer only associates ICE- 1331 related media-level SDP attributes with the "m=" line associated 1332 with the answerer BUNDLE-tag, following the procedures in 1333 Section 8.1. 1335 Support and usage of ICE mechanism together with the BUNDLE extension 1336 is OPTIONAL. 1338 11.1. SDP Offer/Answer Procedures 1340 When an offerer associates a unique address with a bundled "m=" line 1341 (excluding any bundle-only "m=" line), the offerer MUST associate SDP 1342 'candidate' attributes (and other applicable ICE-related media-level 1343 SDP attributes), containing unique ICE properties (candidates etc), 1344 with the "m=" line, according to the procedures in 1345 [I-D.ietf-mmusic-ice-sip-sdp]. 1347 When an offerer associates a shared address with a bundled "m=" line, 1348 the offerer MUST associate SDP 'candidate' attributes (and other 1349 applicable ICE-related media-level SDP attributes) with the "m=" line 1350 following the procedures in Section 8.1. 1352 When an answerer associates a shared address with an "m=" line within 1353 a BUNDLE group, if the answerer MUST associate SDP 'candidate' 1354 attributes (and other applicable ICE-related media-level SDP 1355 attributes) with the "m=" line following the procedures in 1356 Section 8.1. 1358 NOTE: As most ICE-related media-level SDP attributes belong to the 1359 TRANSPORT mux category [I-D.ietf-mmusic-sdp-mux-attributes], the 1360 offerer and answerer follow the procedures in Section 8.1 when 1361 deciding whether to associate an attribute with a bundled "m=" line. 1362 However, in the case of ICE-related media-level attributes, the rules 1363 apply to all attributes (see note below), even if they belong to a 1364 different mux category. 1366 NOTE: The following ICE-related media-level SDP attributes are 1367 defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidiate', 'remote- 1368 candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice- 1369 pacing'. 1371 11.1.1. Generating the Initial SDP Offer 1373 When an offerer generates an initial offer, the offerer MUST 1374 associate ICE-related media-level SDP attributes with bundled "m=" 1375 lines forllowin the procedures in [Section 11.1]. 1377 11.1.2. Generating the SDP Answer 1379 When an answerer generates an answer that contains a BUNDLE group, 1380 the answer MUST associate ICE-related SDP attributes to "m=" lines 1381 within the BUNDLE group according to [Section 11.1]. 1383 11.1.3. Offerer Processing of the SDP Answer 1385 When an offerer receives an answer, if the answerer supports and uses 1386 the ICE mechanism and the BUNDLE extension, the offerer MUST 1387 associate the ICE properties associated with the offerer BUNDLE 1388 address, selected by the answerer [Section 8.3.1], with each bundled 1389 "m=" line. 1391 11.1.4. Modifying the Session 1393 When an offerer generates a subsequent offer, it MUST associate ICE 1394 properties to bundled "m=" lines following the procedures in 1395 [Section 11.1]. 1397 12. DTLS Considerations 1399 One or more media streams within a BUNDLE group might use the 1400 Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order 1401 to encrypt the data, or to negotiate encryption keys if another 1402 encryption mechanism is used to encrypt media. 1404 When DTLS is used within a BUNDLE group, the following rules apply: 1406 o There can only be one DTLS association [RFC6347] associated with 1407 the BUNDLE group; and 1409 o Each usage of the DTLS association within the BUNDLE group MUST 1410 use the same mechanism for determining which endpoints (the 1411 offerer or answerer) become DTLS client and DTLS server; and 1413 o Each usage of the DTLS association within the Bundle group MUST 1414 use the same mechanism for determining whether an offer or answer 1415 will trigger the establishment of a new DTLS association, or 1416 whether an existing DTLS association will be used; and 1418 o If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include 1419 the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message 1420 [RFC5764], The client MUST include the extension even if the usage 1421 of DTLS-SRTP is not negotiated as part of the multimedia session 1422 (e.g., SIP session [RFC3261]. 1424 NOTE: The inclusion of the 'use_srtp' extension during the initial 1425 DTLS handshake ensures that a DTLS renegotiation will not be required 1426 in order to include the extension, in case DTLS-SRTP encrypted media 1427 is added to the BUNDLE group later during the multimedia session. 1429 13. RTP Header Extensions Consideration 1431 When [RFC5285] RTP header extensions are used in the context of this 1432 specification, the identifier used for a given extension MUST 1433 identify the same extension across all the bundled media 1434 descriptions. 1436 14. Update to RFC 3264 1438 This section replaces the text of the following sections of RFC 3264: 1440 o Section 5.1 (Unicast Streams). 1442 o Section 8.2 (Removing a Media Stream). 1444 o Section 8.4 (Putting a Unicast Media Stream on Hold). 1446 14.1. Original text of section 5.1 (2nd paragraph) of RFC 3264 1448 For recvonly and sendrecv streams, the port number and address in the 1449 offer indicate where the offerer would like to receive the media 1450 stream. For sendonly RTP streams, the address and port number 1451 indirectly indicate where the offerer wants to receive RTCP reports. 1452 Unless there is an explicit indication otherwise, reports are sent to 1453 the port number one higher than the number indicated. The IP address 1454 and port present in the offer indicate nothing about the source IP 1455 address and source port of RTP and RTCP packets that will be sent by 1456 the offerer. A port number of zero in the offer indicates that the 1457 stream is offered but MUST NOT be used. This has no useful semantics 1458 in an initial offer, but is allowed for reasons of completeness, 1459 since the answer can contain a zero port indicating a rejected stream 1460 (Section 6). Furthermore, existing streams can be terminated by 1461 setting the port to zero (Section 8). In general, a port number of 1462 zero indicates that the media stream is not wanted. 1464 14.2. New text replacing section 5.1 (2nd paragraph) of RFC 3264 1466 For recvonly and sendrecv streams, the port number and address in the 1467 offer indicate where the offerer would like to receive the media 1468 stream. For sendonly RTP streams, the address and port number 1469 indirectly indicate where the offerer wants to receive RTCP reports. 1470 Unless there is an explicit indication otherwise, reports are sent to 1471 the port number one higher than the number indicated. The IP address 1472 and port present in the offer indicate nothing about the source IP 1473 address and source port of RTP and RTCP packets that will be sent by 1474 the offerer. A port number of zero in the offer by default indicates 1475 that the stream is offered but MUST NOT be used, but an extension 1476 mechanism might specify different semantics for the usage of a zero 1477 port value. Furthermore, existing streams can be terminated by 1478 setting the port to zero (Section 8). In general, a port number of 1479 zero by default indicates that the media stream is not wanted. 1481 14.3. Original text of section 8.2 (2nd paragraph) of RFC 3264 1483 A stream that is offered with a port of zero MUST be marked with port 1484 zero in the answer. Like the offer, the answer MAY omit all 1485 attributes present previously, and MAY list just a single media 1486 format from amongst those in the offer. 1488 14.4. New text replacing section 8.2 (2nd paragraph) of RFC 3264 1490 A stream that is offered with a port of zero MUST by default be 1491 marked with port zero in the answer, unless an extension mechanism, 1492 which specifies semantics for the usage of a non-zero port value, is 1493 used. If the stream is marked with port zero in the answer, the 1494 answer MAY omit all attributes present previously, and MAY list just 1495 a single media format from amongst those in the offer." 1497 14.5. Original text of section 8.4 (6th paragraph) of RFC 3264 1499 RFC 2543 [10] specified that placing a user on hold was accomplished 1500 by setting the connection address to 0.0.0.0. Its usage for putting 1501 a call on hold is no longer recommended, since it doesn't allow for 1502 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1503 with connection oriented media. However, it can be useful in an 1504 initial offer when the offerer knows it wants to use a particular set 1505 of media streams and formats, but doesn't know the addresses and 1506 ports at the time of the offer. Of course, when used, the port 1507 number MUST NOT be zero, which would specify that the stream has been 1508 disabled. An agent MUST be capable of receiving SDP with a 1509 connection address of 0.0.0.0, in which case it means that neither 1510 RTP nor RTCP should be sent to the peer. 1512 14.6. New text replacing section 8.4 (6th paragraph) of RFC 3264 1514 RFC 2543 [10] specified that placing a user on hold was accomplished 1515 by setting the connection address to 0.0.0.0. Its usage for putting 1516 a call on hold is no longer recommended, since it doesn't allow for 1517 RTCP to be used with held streams, doesn't work with IPv6, and breaks 1518 with connection oriented media. However, it can be useful in an 1519 initial offer when the offerer knows it wants to use a particular set 1520 of media streams and formats, but doesn't know the addresses and 1521 ports at the time of the offer. Of course, when used, the port 1522 number MUST NOT be zero, if it would specify that the stream has been 1523 disabled. However, an extension mechanism might specify different 1524 semantics of the zero port number usage. An agent MUST be capable of 1525 receiving SDP with a connection address of 0.0.0.0, in which case it 1526 means that neither RTP nor RTCP should be sent to the peer. 1528 15. RTP/RTCP extensions for identification-tag transport 1530 SDP Offerers and Answerers [RFC3264] can associate identification- 1531 tags with "m=" lines within SDP Offers and Answers, using the 1532 procedures in [RFC5888]. Each identification-tag uniquely represents 1533 an "m=" line. 1535 This section defines a new RTCP SDES item [RFC3550], 'MID', which is 1536 used to carry identification-tags within RTCP SDES packets. This 1537 section also defines a new RTP SDES header extension [RFC7941], which 1538 is used to carry the 'MID' RTCP SDES item in RTP packets. 1540 The SDES item and RTP SDES header extension make it possible for a 1541 receiver to associate each RTP stream with with a specific "m=" line, 1542 with which the receiver has associated an identification-tag, even if 1543 those "m=" lines are part of the same RTP session. The RTP SDES 1544 header extension also ensures that the media recipient gets the 1545 identification-tag upon receipt of the first decodable media and is 1546 able to associate the media with the correct application. 1548 A media recipient informs the media sender about the identification- 1549 tag associated with an "m=" line through the use of an 'mid' 1550 attribute [RFC5888]. The media sender then inserts the 1551 identification-tag in RTCP and RTP packets sent to the media 1552 recipient. 1554 NOTE: This text above defines how identification-tags are carried in 1555 SDP Offers and Answers. The usage of other signalling protocols for 1556 carrying identification-tags is not prevented, but the usage of such 1557 protocols is outside the scope of this document. 1559 [RFC3550] defines general procedures regarding the RTCP transmission 1560 interval. The RTCP MID SDES item SHOULD be sent in the first few 1561 RTCP packets sent after joining the session, and SHOULD be sent 1562 regularly thereafter. The exact number of RTCP packets in which this 1563 SDES item is sent is intentionally not specified here, as it will 1564 depend on the expected packet loss rate, the RTCP reporting interval, 1565 and the allowable overhead. 1567 The RTP SDES header extension for carrying the 'MID' RTCP SDES SHOULD 1568 be included in some RTP packets at the start of the session and 1569 whenever the SSRC changes. It might also be useful to include the 1570 header extension in RTP packets that comprise access points in the 1571 media (e.g., with video I-frames). The exact number of RTP packets 1572 in which this header extension is sent is intentionally not specified 1573 here, as it will depend on expected packet loss rate and loss 1574 patterns, the overhead the application can tolerate, and the 1575 importance of immediate receipt of the identification-tag. 1577 For robustness purpose, endpoints need to be prepared for situations 1578 where the reception of the identification-tag is delayed, and SHOULD 1579 NOT terminate sessions in such cases, as the identification-tag is 1580 likely to arrive soon. 1582 15.1. RTCP MID SDES Item 1584 0 1 2 3 1585 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1587 | MID=TBD | length | identification-tag ... 1588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1590 The identification-tag payload is UTF-8 encoded, as in SDP. 1592 The identification-tag is not zero terminated. 1594 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1595 identifier value.] 1597 15.2. RTP SDES Header Extension For MID 1599 The payload, containing the identification-tag, of the RTP SDES 1600 header extension element can be encoded using either the one-byte or 1601 two-byte header [RFC7941]. The identification-tag payload is UTF-8 1602 encoded, as in SDP. 1604 The identification-tag is not zero terminated. Note, that the set of 1605 header extensions included in the packet needs to be padded to the 1606 next 32-bit boundary using zero bytes [RFC5285]. 1608 As the identification-tag is included in either an RTCP SDES item or 1609 an RTP SDES header extension, or both, there should be some 1610 consideration about the packet expansion caused by the 1611 identification-tag. To avoid Maximum Transmission Unit (MTU) issues 1612 for the RTP packets, the header extension's size needs to be taken 1613 into account when encoding the media. 1615 It is recommended that the identification-tag is kept short. Due to 1616 the properties of the RTP header extension mechanism, when using the 1617 one-byte header, a tag that is 1-3 bytes will result in a minimal 1618 number of 32-bit words used for the RTP SDES header extension, in 1619 case no other header extensions are included at the same time. Note, 1620 do take into account that some single characters when UTF-8 encoded 1621 will result in multiple octets. The identification-tag MUST NOT 1622 contain any user information, and applications SHALL avoid generating 1623 the identification-tag using a pattern that enables application 1624 identification. 1626 16. IANA Considerations 1628 16.1. New SDES item 1630 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1631 document.] 1633 [RFC EDITOR NOTE: Please replace TBD with the assigned SDES 1634 identifier value.] 1636 This document adds the MID SDES item to the IANA "RTP SDES item 1637 types" registry as follows: 1639 Value: TBD 1640 Abbrev.: MID 1641 Name: Media Identification 1642 Reference: RFCXXXX 1644 16.2. New RTP SDES Header Extension URI 1646 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1647 document.] 1648 This document defines a new extension URI in the RTP SDES Compact 1649 Header Extensions sub-registry of the RTP Compact Header Extensions 1650 registry sub-registry, according to the following data: 1652 Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid 1653 Description: Media identification 1654 Contact: christer.holmberg@ericsson.com 1655 Reference: RFCXXXX 1657 The SDES item does not reveal privacy information about the users. 1658 It is simply used to associate RTP-based media with the correct SDP 1659 media description (m- line) in the SDP used to negotiate the media. 1661 The purpose of the extension is for the offerer to be able to 1662 associate received multiplexed RTP-based media before the offerer 1663 receives the associated SDP answer. 1665 16.3. New SDP Attribute 1667 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1668 document.] 1670 This document defines a new SDP media-level attribute, 'bundle-only', 1671 according to the following data: 1673 Attribute name: bundle-only 1674 Type of attribute: media 1675 Subject to charset: No 1676 Purpose: Request a media description to be accepted 1677 in the answer only if kept within a BUNDLE 1678 group by the answerer. 1679 Appropriate values: N/A 1680 Contact name: Christer Holmberg 1681 Contact e-mail: christer.holmberg@ericsson.com 1682 Reference: RFCXXXX 1683 Mux category: NORMAL 1685 16.4. New SDP Group Semantics 1687 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 1688 document.] 1689 This document registers the following semantics with IANA in the 1690 "Semantics for the "group" SDP Attribute" subregistry (under the 1691 "Session Description Protocol (SDP) Parameters" registry: 1693 Semantics Token Reference 1694 ------------------------------------- ------ --------- 1695 Media bundling BUNDLE [RFCXXXX] 1697 17. Security Considerations 1699 The security considerations defined in [RFC3264] and [RFC5888] apply 1700 to the BUNDLE extension. Bundle does not change which information, 1701 e.g., RTP streams, flows over the network, with the exception of the 1702 usage of the MID SDES item as discussed below. Primarily it changes 1703 which addresses and ports, and thus in which (RTP) sessions that the 1704 information is flowing in. This affects the security contexts being 1705 used and can cause previously separated information flows to share 1706 the same security context. This has very little impact on the 1707 performance of the security mechanism of the RTP sessions. In cases 1708 where one would have applied different security policies on the 1709 different RTP streams being bundled, or where the parties having 1710 access to the security contexts would have differed between the RTP 1711 stream, additional analysis of the implications are needed before 1712 selecting to apply BUNDLE. 1714 The identification-tag, independent of transport, RTCP SDES packet or 1715 RTP header extension, can expose the value to parties beyond the 1716 signaling chain. Therefore, the identification-tag values MUST be 1717 generated in a fashion that does not leak user information, e.g., 1718 randomly or using a per-bundle group counter, and SHOULD be 3 bytes 1719 or less, to allow them to efficiently fit into the MID RTP header 1720 extension. Note that if implementations use different methods for 1721 generating identification-tags this could enable fingerprinting of 1722 the implementation making it vulnerable to targeted attacks. The 1723 identification-tag is exposed on the RTP stream level when included 1724 in the RTP header extensions, however what it reveals of the RTP 1725 media stream structure of the endpoint and application was already 1726 possible to deduce from the RTP streams without the MID SDES header 1727 extensions. As the identification-tag is also used to route the 1728 media stream to the right application functionality it is also 1729 important that the value received is the one intended by the sender, 1730 thus integrity and the authenticity of the source are important to 1731 prevent denial of service on the application. Existing SRTP 1732 configurations and other security mechanisms protecting the whole 1733 RTP/RTCP packets will provide the necessary protection. 1735 When the BUNDLE extension is used, the set of configurations of the 1736 security mechanism used in all the bundled media descriptions will 1737 need to be compatible so that they can simultaneously used in 1738 parallel, at least per direction or endpoint. When using SRTP this 1739 will be the case, at least for the IETF defined key-management 1740 solutions due to their SDP attributes (a=crypto, a=fingerprint, 1741 a=mikey) and their classification in 1742 [I-D.ietf-mmusic-sdp-mux-attributes]. 1744 The security considerations of "RTP Header Extension for the RTP 1745 Control Protocol (RTCP) Source Description Items" [RFC7941] requires 1746 that when RTCP is confidentiality protected that any SDES RTP header 1747 extension carrying an SDES item, such as the MID RTP header 1748 extension, is also protected using commensurate strength algorithms. 1749 However, assuming the above requirements and recommendations are 1750 followed there are no known significant security risks with leaving 1751 the MID RTP header extension without confidentiality protection. 1752 Thus, the requirements in RFC 7941 MAY be ignored for the MID RTP 1753 header extension. Security mechanisms for RTP/RTCP are discussed in 1754 Options for Securing RTP Sessions [RFC7201], for example SRTP 1755 [RFC3711] can provide the necessary security functions of ensuring 1756 the integrity and source authenticity. 1758 18. Examples 1760 18.1. Example: Bundle Address Selection 1762 The example below shows: 1764 o An offer, in which the offerer associates a unique address with 1765 each bundled "m=" line within the BUNDLE group. 1767 o An answer, in which the answerer selects the offerer BUNDLE 1768 address, and then selects its own BUNDLE address (the answerer 1769 BUNDLE address) and associates it with each bundled "m=" line 1770 within the BUNDLE group. 1772 SDP Offer (1) 1774 v=0 1775 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1776 s= 1777 c=IN IP4 atlanta.example.com 1778 t=0 0 1779 a=group:BUNDLE foo bar 1780 m=audio 10000 RTP/AVP 0 8 97 1781 b=AS:200 1782 a=mid:foo 1783 a=rtcp-mux 1784 a=rtpmap:0 PCMU/8000 1785 a=rtpmap:8 PCMA/8000 1786 a=rtpmap:97 iLBC/8000 1787 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1788 m=video 10002 RTP/AVP 31 32 1789 b=AS:1000 1790 a=mid:bar 1791 a=rtcp-mux 1792 a=rtpmap:31 H261/90000 1793 a=rtpmap:32 MPV/90000 1794 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1796 SDP Answer (2) 1798 v=0 1799 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1800 s= 1801 c=IN IP4 biloxi.example.com 1802 t=0 0 1803 a=group:BUNDLE foo bar 1804 m=audio 20000 RTP/AVP 0 1805 b=AS:200 1806 a=mid:foo 1807 a=rtcp-mux 1808 a=rtpmap:0 PCMU/8000 1809 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1810 m=video 20000 RTP/AVP 32 1811 b=AS:1000 1812 a=mid:bar 1813 a=rtpmap:32 MPV/90000 1814 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1816 18.2. Example: BUNDLE Extension Rejected 1818 The example below shows: 1820 o An offer, in which the offerer associates a unique address with 1821 each bundled "m=" line within the BUNDLE group. 1823 o An answer, in which the answerer rejects the offered BUNDLE group, 1824 and associates a unique address with each "m=" line (following 1825 normal RFC 3264 procedures). 1827 SDP Offer (1) 1829 v=0 1830 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1831 s= 1832 c=IN IP4 atlanta.example.com 1833 t=0 0 1834 a=group:BUNDLE foo bar 1835 m=audio 10000 RTP/AVP 0 8 97 1836 b=AS:200 1837 a=mid:foo 1838 a=rtcp-mux 1839 a=rtpmap:0 PCMU/8000 1840 a=rtpmap:8 PCMA/8000 1841 a=rtpmap:97 iLBC/8000 1842 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1843 m=video 10002 RTP/AVP 31 32 1844 b=AS:1000 1845 a=mid:bar 1846 a=rtcp-mux 1847 a=rtpmap:31 H261/90000 1848 a=rtpmap:32 MPV/90000 1849 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1851 SDP Answer (2) 1853 v=0 1854 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1855 s= 1856 c=IN IP4 biloxi.example.com 1857 t=0 0 1858 m=audio 20000 RTP/AVP 0 1859 b=AS:200 1860 a=rtcp-mux 1861 a=rtpmap:0 PCMU/8000 1862 m=video 30000 RTP/AVP 32 1863 b=AS:1000 1864 a=rtcp-mux 1865 a=rtpmap:32 MPV/90000 1867 18.3. Example: Offerer Adds A Media Description To A BUNDLE Group 1869 The example below shows: 1871 o A subsequent offer (the BUNDLE group has been created as part of a 1872 previous offer/answer exchange), in which the offerer adds a new 1873 "m=" line, represented by the "zen" identification-tag, to a 1874 previously negotiated BUNDLE group, associates a unique address 1875 with the added "m=" line, and associates the previously selected 1876 offerer BUNDLE address with each of the other bundled "m=" lines 1877 within the BUNDLE group. 1879 o An answer, in which the answerer associates the answerer BUNDLE 1880 address with each bundled "m=" line (including the newly added 1881 "m=" line) within the BUNDLE group. 1883 SDP Offer (1) 1885 v=0 1886 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1887 s= 1888 c=IN IP4 atlanta.example.com 1889 t=0 0 1890 a=group:BUNDLE foo bar zen 1891 m=audio 10000 RTP/AVP 0 8 97 1892 b=AS:200 1893 a=mid:foo 1894 a=rtcp-mux 1895 a=rtpmap:0 PCMU/8000 1896 a=rtpmap:8 PCMA/8000 1897 a=rtpmap:97 iLBC/8000 1898 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1899 m=video 10000 RTP/AVP 31 32 1900 b=AS:1000 1901 a=mid:bar 1902 a=rtpmap:31 H261/90000 1903 a=rtpmap:32 MPV/90000 1904 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1905 m=video 20000 RTP/AVP 66 1906 b=AS:1000 1907 a=mid:zen 1908 a=rtcp-mux 1909 a=rtpmap:66 H261/90000 1910 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1912 SDP Answer (2) 1914 v=0 1915 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1916 s= 1917 c=IN IP4 biloxi.example.com 1918 t=0 0 1919 a=group:BUNDLE foo bar zen 1920 m=audio 20000 RTP/AVP 0 1921 b=AS:200 1922 a=mid:foo 1923 a=rtcp-mux 1924 a=rtpmap:0 PCMU/8000 1925 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1926 m=video 20000 RTP/AVP 32 1927 b=AS:1000 1928 a=mid:bar 1929 a=rtpmap:32 MPV/90000 1930 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1931 m=video 20000 RTP/AVP 66 1932 b=AS:1000 1933 a=mid:zen 1934 a=rtpmap:66 H261/90000 1935 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1937 18.4. Example: Offerer Moves A Media Description Out Of A BUNDLE Group 1939 The example below shows: 1941 o A subsequent offer (the BUNDLE group has been created as part of a 1942 previous offer/answer transaction), in which the offerer moves a 1943 bundled "m=" line out of a BUNDLE group, associates a unique 1944 address with the moved "m=" line, and associates the offerer 1945 BUNDLE address with each other bundled "m=" line within the BUNDLE 1946 group. 1948 o An answer, in which the answerer moves the "m=" line out of the 1949 BUNDLE group, associates a unique address with the moved "m=" 1950 line, and associates the answerer BUNDLE address with each of the 1951 remaining bundled "m=" line within the BUNDLE group. 1953 SDP Offer (1) 1955 v=0 1956 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 1957 s= 1958 c=IN IP4 atlanta.example.com 1959 t=0 0 1960 a=group:BUNDLE foo bar 1961 m=audio 10000 RTP/AVP 0 8 97 1962 b=AS:200 1963 a=mid:foo 1964 a=rtcp-mux 1965 a=rtpmap:0 PCMU/8000 1966 a=rtpmap:8 PCMA/8000 1967 a=rtpmap:97 iLBC/8000 1968 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1969 m=video 10000 RTP/AVP 31 32 1970 b=AS:1000 1971 a=mid:bar 1972 a=rtpmap:31 H261/90000 1973 a=rtpmap:32 MPV/90000 1974 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1975 m=video 50000 RTP/AVP 66 1976 b=AS:1000 1977 a=mid:zen 1978 a=rtcp-mux 1979 a=rtpmap:66 H261/90000 1981 SDP Answer (2) 1983 v=0 1984 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 1985 s= 1986 c=IN IP4 biloxi.example.com 1987 t=0 0 1988 a=group:BUNDLE foo bar 1989 m=audio 20000 RTP/AVP 0 1990 b=AS:200 1991 a=mid:foo 1992 a=rtcp-mux 1993 a=rtpmap:0 PCMU/8000 1994 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 1995 m=video 20000 RTP/AVP 32 1996 b=AS:1000 1997 a=mid:bar 1998 a=rtpmap:32 MPV/90000 1999 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2000 m=video 60000 RTP/AVP 66 2001 b=AS:1000 2002 a=mid:zen 2003 a=rtcp-mux 2004 a=rtpmap:66 H261/90000 2006 18.5. Example: Offerer Disables A Media Description Within A BUNDLE 2007 Group 2009 The example below shows: 2011 o A subsequent offer (the BUNDLE group has been created as part of a 2012 previous offer/answer transaction), in which the offerer disables 2013 a bundled "m=" line within a BUNDLE group, assigns a zero port 2014 number to the disabled "m=" line, and associates the offerer 2015 BUNDLE address with each of the other bundled "m=" lines within 2016 the BUNDLE group. 2018 o An answer, in which the answerer moves the disabled "m=" line out 2019 of the BUNDLE group, assigns a zero port value to the disabled 2020 "m=" line, and associates the answerer BUNDLE address with each of 2021 the remaining bundled "m=" line within the BUNDLE group. 2023 SDP Offer (1) 2025 v=0 2026 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2027 s= 2028 c=IN IP4 atlanta.example.com 2029 t=0 0 2030 a=group:BUNDLE foo bar 2031 m=audio 10000 RTP/AVP 0 8 97 2032 b=AS:200 2033 a=mid:foo 2034 a=rtcp-mux 2035 a=rtpmap:0 PCMU/8000 2036 a=rtpmap:8 PCMA/8000 2037 a=rtpmap:97 iLBC/8000 2038 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2039 m=video 10000 RTP/AVP 31 32 2040 b=AS:1000 2041 a=mid:bar 2042 a=rtpmap:31 H261/90000 2043 a=rtpmap:32 MPV/90000 2044 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2045 m=video 0 RTP/AVP 66 2046 a=mid:zen 2047 a=rtpmap:66 H261/90000 2049 SDP Answer (2) 2051 v=0 2052 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2053 s= 2054 c=IN IP4 biloxi.example.com 2055 t=0 0 2056 a=group:BUNDLE foo bar 2057 m=audio 20000 RTP/AVP 0 2058 b=AS:200 2059 a=mid:foo 2060 a=rtcp-mux 2061 a=rtpmap:0 PCMU/8000 2062 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2063 m=video 20000 RTP/AVP 32 2064 b=AS:1000 2065 a=mid:bar 2066 a=rtpmap:32 MPV/90000 2067 a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid 2068 m=video 0 RTP/AVP 66 2069 a=mid:zen 2070 a=rtpmap:66 H261/90000 2072 19. Acknowledgements 2074 The usage of the SDP grouping extension for negotiating bundled media 2075 is based on a similar alternatives proposed by Harald Alvestrand and 2076 Cullen Jennings. The BUNDLE extension described in this document is 2077 based on the different alternative proposals, and text (e.g., SDP 2078 examples) have been borrowed (and, in some cases, modified) from 2079 those alternative proposals. 2081 The SDP examples are also modified versions from the ones in the 2082 Alvestrand proposal. 2084 Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas 2085 Stach, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount, 2086 Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and 2087 Justin Uberti for reading the text, and providing useful feedback. 2089 Thanks to Bernard Aboba, Cullen Jennings, Peter Thatcher, Justin 2090 Uberti, and Magnus Westerlund for providing the text for the section 2091 on RTP/RTCP stream association. 2093 Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for 2094 providing help and text on the RTP/RTCP procedures. 2096 Thanks to Spotify for providing music for the countless hours of 2097 document editing. 2099 20. Change Log 2101 [RFC EDITOR NOTE: Please remove this section when publishing] 2103 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-38 2105 o Changes to RTP streaming mapping section based on text from Colin 2106 Perkins. 2108 o The following GitHub pull requests were merged: 2110 o https://github.com/cdh4u/draft-sdp-bundle/pull/34 2112 o - Proposed updates to RTP processing 2114 o https://github.com/cdh4u/draft-sdp-bundle/pull/35 2116 o - fixed reference to receiver-id section 2118 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-37 2120 o The following GitHub pull request was merged: 2122 o https://github.com/cdh4u/draft-sdp-bundle/pull/33 2124 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-36 2126 o The following GitHub pull requests were merged: 2128 o https://github.com/cdh4u/draft-sdp-bundle/pull/32 2130 o - extmap handling in BUNDLE. 2132 o https://github.com/cdh4u/draft-sdp-bundle/pull/31 2134 o - Additional Acknowledgement text added. 2136 o https://github.com/cdh4u/draft-sdp-bundle/pull/30 2138 o - MID SDES item security procedures updated 2140 o https://github.com/cdh4u/draft-sdp-bundle/pull/29 2142 o - Appendix B of JSEP moved into BUNDLE. 2144 o - Associating RTP/RTCP packets with SDP m- lines. 2146 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-35 2147 o Editorial changes on RTP streaming mapping section based on 2148 comments from Colin Perkins. 2150 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-34 2152 o RTP streams, instead of RTP packets, are associated with m- lines. 2154 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-33 2156 o Editorial changes based on comments from Eric Rescorla and Cullen 2157 Jennings: 2159 o - Changes regarding usage of RTP/RTCP multiplexing attributes. 2161 o - Additional text regarding associating RTP/RTCP packets with SDP 2162 m- lines. 2164 o - Reference correction. 2166 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-32 2168 o Editorial changes based on comments from Eric Rescorla and Cullen 2169 Jennings: 2171 o - Justification for mechanism added to Introduction. 2173 o - Clarify that the order of m- lines in the group:BUNDLE attribute 2174 does not have to be the same as the order in which the m- lines 2175 are listed in the SDP. 2177 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-31 2179 o Editorial changes based on GitHub Pull requests by Martin Thomson: 2181 o - https://github.com/cdh4u/draft-sdp-bundle/pull/2 2183 o - https://github.com/cdh4u/draft-sdp-bundle/pull/1 2185 o Editorial change based on comment from Diederick Huijbers (9th 2186 July 2016). 2188 o Changes based on comments from Flemming Andreasen (21st June 2189 2016): 2191 o - Mux category for SDP bundle-only attribute added. 2193 o - Mux category considerations editorial clarification. 2195 o - Editorial changes. 2197 o RTP SDES extension according to draft-ietf-avtext-sdes-hdr-ext. 2199 o Note whether Design Considerations appendix is to be kept removed: 2201 o - Appendix is kept within document. 2203 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-30 2205 o Indicating in the Abstract and Introduction that the document 2206 updates RFC 3264. 2208 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-29 2210 o Change based on WGLC comment from Colin Perkins. 2212 o - Clarify that SSRC can be reused by another source after a delay 2213 of 5 RTCP reporting intervals. 2215 o Change based on WGLC comment from Alissa Cooper. 2217 o - IANA registry name fix. 2219 o - Additional IANA registration information added. 2221 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-28 2223 o - Alignment with exclusive mux procedures. 2225 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-27 2227 o - Yet another terminology change. 2229 o - Mux category considerations added. 2231 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26 2233 o - ICE considerations modified: ICE-related SDP attributes only 2234 added to the bundled m- line representing the selected BUNDLE 2235 address. 2237 o - Reference to draft-ietf-mmusic-ice-sip-sdp added. 2239 o - Reference to RFC 5245 replaced with reference to draft-ietf-ice- 2240 rfc5245bis. 2242 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25 2243 o - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux 2244 considerations. 2246 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24 2248 o - Reference and procedures associated with exclusive RTP/RTCP mux 2249 added 2251 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23 2253 o - RTCP-MUX mandatory for bundled RTP m- lines 2255 o - Editorial fixes based on comments from Flemming Andreasen 2257 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22 2259 o - Correction of Ari's family name 2261 o - Editorial fixes based on comments from Thomas Stach 2263 o - RTP/RTCP correction based on comment from Magnus Westerlund 2265 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 2266 msg14861.html 2268 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21 2270 o - Correct based on comment from Paul Kyzivat 2272 o -- 'received packets' replaced with 'received data' 2274 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20 2276 o - Clarification based on comment from James Guballa 2278 o - Clarification based on comment from Flemming Andreasen 2280 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19 2282 o - DTLS Considerations section added. 2284 o - BUNDLE semantics added to the IANA Considerations 2286 o - Changes based on WGLC comments from Adam Roach 2288 o -- http://www.ietf.org/mail-archive/web/mmusic/current/ 2289 msg14673.html 2291 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18 2293 o - Changes based on agreements at IETF#92 2295 o -- BAS Offer removed, based on agreement at IETF#92. 2297 o -- Procedures regarding usage of SDP "b=" line is replaced with a 2298 reference to to draft-ietf-mmusic-sdp-mux-attributes. 2300 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17 2302 o - Editorial changes based on comments from Magnus Westerlund. 2304 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16 2306 o - Modification of RTP/RTCP multiplexing section, based on comments 2307 from Magnus Westerlund. 2309 o - Reference updates. 2311 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15 2313 o - Editorial fix. 2315 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14 2317 o - Editorial changes. 2319 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13 2321 o Changes to allow a new suggested offerer BUNDLE address to be 2322 assigned to each bundled m- line. 2324 o Changes based on WGLC comments from Paul Kyzivat 2326 o - Editorial fixes 2328 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12 2330 o Usage of SDP 'extmap' attribute added 2332 o SDP 'bundle-only' attribute scoped with "m=" lines with a zero 2333 port value 2335 o Changes based on WGLC comments from Thomas Stach 2337 o - ICE candidates not assigned to bundle-only m- lines with a zero 2338 port value 2340 o - Editorial changes 2342 o Changes based on WGLC comments from Colin Perkins 2344 o - Editorial changes: 2346 o -- "RTP SDES item" -> "RTCP SDES item" 2348 o -- "RTP MID SDES item" -> "RTCP MID SDES item" 2350 o - Changes in section 10.1.1: 2352 o -- "SHOULD NOT" -> "MUST NOT" 2354 o -- Additional text added to the Note 2356 o - Change to section 13.2: 2358 o -- Clarify that mid value is not zero terminated 2360 o - Change to section 13.3: 2362 o -- Clarify that mid value is not zero terminated 2364 o -- Clarify padding 2366 o Changes based on WGLC comments from Paul Kyzivat 2368 o - Editorial changes: 2370 o Changes based on WGLC comments from Jonathan Lennox 2372 o - Editorial changes: 2374 o - Defintion of SDP bundle-only attribute alligned with structure 2375 in 4566bis draft 2377 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11 2379 o Editorial corrections based on comments from Harald Alvestrand. 2381 o Editorial corrections based on comments from Cullen Jennings. 2383 o Reference update (RFC 7160). 2385 o Clarification about RTCP packet sending when RTP/RTCP multiplexing 2386 is not used (http://www.ietf.org/mail-archive/web/mmusic/current/ 2387 msg13765.html). 2389 o Additional text added to the Security Considerations. 2391 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10 2393 o SDP bundle-only attribute added to IANA Considerations. 2395 o SDES item and RTP header extension added to Abstract and 2396 Introduction. 2398 o Modification to text updating section 8.2 of RFC 3264. 2400 o Reference corrections. 2402 o Editorial corrections. 2404 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09 2406 o Terminology change: "bundle-only attribute assigned to m= line" to 2407 "bundle-only attribute associated with m= line". 2409 o Editorial corrections. 2411 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08 2413 o Editorial corrections. 2415 o - "of"->"if" (8.3.2.5). 2417 o - "optional"->"OPTIONAL" (9.1). 2419 o - Syntax/ABNF for 'bundle-only' attribute added. 2421 o - SDP Offer/Answer sections merged. 2423 o - 'Request new offerer BUNDLE address' section added 2425 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07 2427 o OPEN ISSUE regarding Receiver-ID closed. 2429 o - RTP MID SDES Item. 2431 o - RTP MID Header Extension. 2433 o OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers 2434 closed. 2436 o - Indicating that, when rtcp-mux is used, the answerer MUST NOT 2437 include an 'rtcp' attribute in the answer, based on the procedures 2438 in section 5.1.3 of RFC 5761. 2440 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06 2442 o Draft title changed. 2444 o Added "SDP" to section names containing "Offer" or "Answer". 2446 o Editorial fixes based on comments from Paul Kyzivat 2447 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2448 msg13314.html). 2450 o Editorial fixed based on comments from Colin Perkins 2451 (http://www.ietf.org/mail-archive/web/mmusic/current/ 2452 msg13318.html). 2454 o - Removed text about extending BUNDLE to allow multiple RTP 2455 sessions within a BUNDLE group. 2457 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05 2459 o Major re-structure of SDP Offer/Answer sections, to align with RFC 2460 3264 structure. 2462 o Additional definitions added. 2464 o - Shared address. 2466 o - Bundled "m=" line. 2468 o - Bundle-only "m=" line. 2470 o - Offerer suggested BUNDLE mid. 2472 o - Answerer selected BUNDLE mid. 2474 o Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address 2475 to multiple "m=" lines until it has received an SDP Answer 2476 indicating support of the BUNDLE extension. 2478 o Q8 Closed (IETF#88): An Offerer can, before it knows whether the 2479 Answerer supports the BUNDLE extension, assign a zero port value 2480 to a 'bundle-only' "m=" line. 2482 o SDP 'bundle-only' attribute section added. 2484 o Connection data nettype/addrtype restrictions added. 2486 o RFC 3264 update section added. 2488 o Indicating that a specific payload type value can be used in 2489 multiple "m=" lines, if the value represents the same codec 2490 configuration in each "m=" line. 2492 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04 2494 o Updated Offerer procedures (http://www.ietf.org/mail- 2495 archive/web/mmusic/current/msg12293.html). 2497 o Updated Answerer procedures (http://www.ietf.org/mail- 2498 archive/web/mmusic/current/msg12333.html). 2500 o Usage of SDP 'bundle-only' attribute added. 2502 o Reference to Trickle ICE document added. 2504 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02 2506 o Mechanism modified, to be based on usage of SDP Offers with both 2507 different and identical port number values, depending on whether 2508 it is known if the remote endpoint supports the extension. 2510 o Cullen Jennings added as co-author. 2512 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01 2514 o No changes. New version due to expiration. 2516 Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00 2518 o No changes. New version due to expiration. 2520 Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00 2522 o Draft name changed. 2524 o Harald Alvestrand added as co-author. 2526 o "Multiplex" terminology changed to "bundle". 2528 o Added text about single versus multiple RTP Sessions. 2530 o Added reference to RFC 3550. 2532 21. References 2534 21.1. Normative References 2536 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2537 Requirement Levels", BCP 14, RFC 2119, 2538 DOI 10.17487/RFC2119, March 1997, . 2541 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 2542 with Session Description Protocol (SDP)", RFC 3264, 2543 DOI 10.17487/RFC3264, June 2002, . 2546 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 2547 Jacobson, "RTP: A Transport Protocol for Real-Time 2548 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 2549 July 2003, . 2551 [RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute 2552 in Session Description Protocol (SDP)", RFC 3605, 2553 DOI 10.17487/RFC3605, October 2003, . 2556 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 2557 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 2558 RFC 3711, DOI 10.17487/RFC3711, March 2004, 2559 . 2561 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 2562 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 2563 July 2006, . 2565 [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", 2566 BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, 2567 . 2569 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 2570 (ICE): A Protocol for Network Address Translator (NAT) 2571 Traversal for Offer/Answer Protocols", RFC 5245, 2572 DOI 10.17487/RFC5245, April 2010, . 2575 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 2576 Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2577 2008, . 2579 [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and 2580 Control Packets on a Single Port", RFC 5761, 2581 DOI 10.17487/RFC5761, April 2010, . 2584 [RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer 2585 Security (DTLS) Extension to Establish Keys for the Secure 2586 Real-time Transport Protocol (SRTP)", RFC 5764, 2587 DOI 10.17487/RFC5764, May 2010, . 2590 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 2591 Protocol (SDP) Grouping Framework", RFC 5888, 2592 DOI 10.17487/RFC5888, June 2010, . 2595 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2596 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2597 January 2012, . 2599 [RFC7941] Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP 2600 Header Extension for the RTP Control Protocol (RTCP) 2601 Source Description Items", RFC 7941, DOI 10.17487/RFC7941, 2602 August 2016, . 2604 [I-D.ietf-ice-rfc5245bis] 2605 Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive 2606 Connectivity Establishment (ICE): A Protocol for Network 2607 Address Translator (NAT) Traversal", draft-ietf-ice- 2608 rfc5245bis-10 (work in progress), May 2017. 2610 [I-D.ietf-mmusic-sdp-mux-attributes] 2611 Nandakumar, S., "A Framework for SDP Attributes when 2612 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 2613 (work in progress), December 2016. 2615 [I-D.ietf-mmusic-mux-exclusive] 2616 Holmberg, C., "Indicating Exclusive Support of RTP/RTCP 2617 Multiplexing using SDP", draft-ietf-mmusic-mux- 2618 exclusive-12 (work in progress), May 2017. 2620 [I-D.ietf-mmusic-ice-sip-sdp] 2621 Petit-Huguenin, M., Keranen, A., and S. Nandakumar, 2622 "Session Description Protocol (SDP) Offer/Answer 2623 procedures for Interactive Connectivity Establishment 2624 (ICE)", draft-ietf-mmusic-ice-sip-sdp-13 (work in 2625 progress), June 2017. 2627 21.2. Informative References 2629 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 2630 A., Peterson, J., Sparks, R., Handley, M., and E. 2631 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 2632 DOI 10.17487/RFC3261, June 2002, . 2635 [RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., 2636 "RTP Control Protocol Extended Reports (RTCP XR)", 2637 RFC 3611, DOI 10.17487/RFC3611, November 2003, 2638 . 2640 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 2641 "Codec Control Messages in the RTP Audio-Visual Profile 2642 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 2643 February 2008, . 2645 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 2646 "Extended RTP Profile for Real-time Transport Control 2647 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 2648 DOI 10.17487/RFC4585, July 2006, . 2651 [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific 2652 Media Attributes in the Session Description Protocol 2653 (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, 2654 . 2656 [RFC7160] Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple 2657 Clock Rates in an RTP Session", RFC 7160, 2658 DOI 10.17487/RFC7160, April 2014, . 2661 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 2662 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 2663 . 2665 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 2666 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 2667 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 2668 DOI 10.17487/RFC7656, November 2015, . 2671 [I-D.ietf-ice-trickle] 2672 Ivov, E., Rescorla, E., Uberti, J., and P. Saint-Andre, 2673 "Trickle ICE: Incremental Provisioning of Candidates for 2674 the Interactive Connectivity Establishment (ICE) 2675 Protocol", draft-ietf-ice-trickle-13 (work in progress), 2676 July 2017. 2678 [I-D.ietf-avtext-lrr] 2679 Lennox, J., Hong, D., Uberti, J., Holmer, S., and M. 2680 Flodman, "The Layer Refresh Request (LRR) RTCP Feedback 2681 Message", draft-ietf-avtext-lrr-07 (work in progress), 2682 July 2017. 2684 Appendix A. Design Considerations 2686 One of the main issues regarding the BUNDLE grouping extensions has 2687 been whether, in SDP Offers and SDP Answers, the same port value 2688 should be inserted in "m=" lines associated with a BUNDLE group, as 2689 the purpose of the extension is to negotiate the usage of a single 2690 address:port combination for media specified by the "m=" lines. 2691 Issues with both approaches, discussed in the Appendix have been 2692 raised. The outcome was to specify a mechanism which uses SDP Offers 2693 with both different and identical port values. 2695 Below are the primary issues that have been considered when defining 2696 the "BUNDLE" grouping extension: 2698 o 1) Interoperability with existing UAs. 2700 o 2) Interoperability with intermediary B2BUA- and proxy entities. 2702 o 3) Time to gather, and the number of, ICE candidates. 2704 o 4) Different error scenarios, and when they occur. 2706 o 5) SDP Offer/Answer impacts, including usage of port number value 2707 zero. 2709 A.1. UA Interoperability 2711 Consider the following SDP Offer/Answer exchange, where Alice sends 2712 an SDP Offer to Bob: 2714 SDP Offer 2716 v=0 2717 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2718 s= 2719 c=IN IP4 atlanta.example.com 2720 t=0 0 2721 m=audio 10000 RTP/AVP 97 2722 a=rtpmap:97 iLBC/8000 2723 m=video 10002 RTP/AVP 97 2724 a=rtpmap:97 H261/90000 2726 SDP Answer 2728 v=0 2729 o=bob 2808844564 2808844564 IN IP4 biloxi.example.com 2730 s= 2731 c=IN IP4 biloxi.example.com 2732 t=0 0 2733 m=audio 20000 RTP/AVP 97 2734 a=rtpmap:97 iLBC/8000 2735 m=video 20002 RTP/AVP 97 2736 a=rtpmap:97 H261/90000 2738 RFC 4961 specifies a way of doing symmetric RTP but that is an a 2739 later invention to RTP and Bob can not assume that Alice supports RFC 2740 4961. This means that Alice may be sending RTP from a different port 2741 than 10000 or 10002 - some implementation simply send the RTP from an 2742 ephemeral port. When Bob's endpoint receives an RTP packet, the only 2743 way that Bob knows if it should be passed to the video or audio codec 2744 is by looking at the port it was received on. This lead some SDP 2745 implementations to use the fact that each "m=" line had a different 2746 port number to use that port number as an index to find the correct m 2747 line in the SDP. As a result, some implementations that do support 2748 symmetric RTP and ICE still use a SDP data structure where SDP with 2749 "m=" lines with the same port such as: 2751 SDP Offer 2753 v=0 2754 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2755 s= 2756 c=IN IP4 atlanta.example.com 2757 t=0 0 2758 m=audio 10000 RTP/AVP 97 2759 a=rtpmap:97 iLBC/8000 2760 m=video 10000 RTP/AVP 98 2761 a=rtpmap:98 H261/90000 2763 will result in the second "m=" line being considered an SDP error 2764 because it has the same port as the first line. 2766 A.2. Usage of port number value zero 2768 In an SDP Offer or SDP Answer, the media specified by an "m=" line 2769 can be disabled/rejected by setting the port number value to zero. 2770 This is different from e.g., using the SDP direction attributes, 2771 where RTCP traffic will continue even if the SDP "inactive" attribute 2772 is indicated for the associated "m=" line. 2774 If each "m=" line associated with a BUNDLE group would contain 2775 different port values, and one of those port values would be used for 2776 a BUNDLE address associated with the BUNDLE group, problems would 2777 occur if an endpoint wants to disable/reject the "m=" line associated 2778 with that port, by setting the port value to zero. After that, no 2779 "m=" line would contain the port value which is used for the BUNDLE 2780 address. In addition, it is unclear what would happen to the ICE 2781 candidates associated with the "m=" line, as they are also used for 2782 the BUNDLE address. 2784 A.3. B2BUA And Proxy Interoperability 2786 Some back to back user agents may be configured in a mode where if 2787 the incoming call leg contains an SDP attribute the B2BUA does not 2788 understand, the B2BUA still generates that SDP attribute in the Offer 2789 for the outgoing call leg. Consider a B2BUA that did not understand 2790 the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way. 2791 Further assume that the B2BUA was configured to tear down any call 2792 where it did not see any RTCP for 5 minutes. In this case, if the 2793 B2BUA received an Offer like: 2795 SDP Offer 2797 v=0 2798 o=alice 2890844526 2890844526 IN IP4 atlanta.example.com 2799 s= 2800 c=IN IP4 atlanta.example.com 2801 t=0 0 2802 m=audio 49170 RTP/AVP 0 2803 a=rtcp:53020 2805 It would be looking for RTCP on port 49172 but would not see any 2806 because the RTCP would be on port 53020 and after five minutes, it 2807 would tear down the call. Similarly, a B2BUA that did not understand 2808 BUNDLE yet put BUNDLE in it's offer may be looking for media on the 2809 wrong port and tear down the call. It is worth noting that a B2BUA 2810 that generated an Offer with capabilities it does not understand is 2811 not compliant with the specifications. 2813 A.3.1. Traffic Policing 2815 Sometimes intermediaries do not act as B2BUA, in the sense that they 2816 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2817 however, they may use SDP information (e.g., IP address and port) in 2818 order to control traffic gating functions, and to set traffic 2819 policing rules. There might be rules which will trigger a session to 2820 be terminated in case media is not sent or received on the ports 2821 retrieved from the SDP. This typically occurs once the session is 2822 already established and ongoing. 2824 A.3.2. Bandwidth Allocation 2826 Sometimes intermediaries do not act as B2BUA, in the sense that they 2827 don't modify SDP bodies, nor do they terminate SIP dialogs. Still, 2828 however, they may use SDP information (e.g., codecs and media types) 2829 in order to control bandwidth allocation functions. The bandwidth 2830 allocation is done per "m=" line, which means that it might not be 2831 enough if media specified by all "m=" lines try to use that 2832 bandwidth. That may either simply lead to bad user experience, or to 2833 termination of the call. 2835 A.4. Candidate Gathering 2837 When using ICE, a candidate needs to be gathered for each port. This 2838 takes approximately 20 ms extra for each extra "m=" line due to the 2839 NAT pacing requirements. All of this gather can be overlapped with 2840 other things while for exampe a web-page is loading to minimize the 2841 impact. If the client only wants to generate TURN or STUN ICE 2842 candidates for one of the "m=" lines and then use trickle ICE 2843 [I-D.ietf-ice-trickle] to get the non host ICE candidates for the 2844 rest of the "m=" lines, it MAY do that and will not need any 2845 additional gathering time. 2847 Some people have suggested a TURN extension to get a bunch of TURN 2848 allocations at once. This would only provide a single STUN result so 2849 in cases where the other end did not support BUNDLE, may cause more 2850 use of the TURN server but would be quick in the cases where both 2851 sides supported BUNDLE and would fall back to a successful call in 2852 the other cases. 2854 Authors' Addresses 2856 Christer Holmberg 2857 Ericsson 2858 Hirsalantie 11 2859 Jorvas 02420 2860 Finland 2862 Email: christer.holmberg@ericsson.com 2864 Harald Tveit Alvestrand 2865 Google 2866 Kungsbron 2 2867 Stockholm 11122 2868 Sweden 2870 Email: harald@alvestrand.no 2872 Cullen Jennings 2873 Cisco 2874 400 3rd Avenue SW, Suite 350 2875 Calgary, AB T2P 4H2 2876 Canada 2878 Email: fluffy@iii.ca